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tBy 3 H. HALLE ERG 



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COPYRIGHT DEPOSIT. 



MOTION PICTURE 

ELECTRICITY 



By jr HV 1 HALLBERG 



Published by 
THE MOVING PICTURE WORLD 

Pullman Building, 17 Madison Avenue 
NEW YORK CITY 



^2 



Copyright in the United States, 1914 

Copyright in Great Britain, 1914 

Copyright in Canada, 1914 

by 

J. H. HALLBERG 

New York 
All Rights Reserved 



CI.A387319. 




J. H. HALLBERG 



The Author 



IN an issue of the Electrical World of July 15, 
1905, the following biographical sketch was first 
published : 

"Josef Henrik Hallberg was born in Falkenberg, 
Sweden, in the year 1874. In the spring of 1890 he 
graduated from Latin-Laroverket, Halmsted, Sweden. 
Shortly thereafter he came to America, and in October 
of the same year entered the Ottumwa Iron Works, 
Ottumwa, Iowa, as apprentice in the machinist trade. 
During the three years of his apprenticeship he gained 
much practical experience in building and testing, erect- 
ing and operating steam engines, coal mining and hoist- 
ing machinery. 

"After completing the apprenticeship course in 1893, 
he became associated with Kohler Brothers, contracting 
engineers in Chicago, which connection he severed in 
1894 to accept a position as sales engineer with the Elec- 
tric Appliance Company, of Chicago, with which com- 
pany he remained until 1896. For three years, or until 
1899, ne served as electrical engineer and designer for 
the Standard Thermometer & Electric Company, Pea- 
body, Mass. 

"From 1899 until 1903 he was electric engineer and 
designer with the General Incandescent Arc Light Com- 
pany, New York. While with this company he patented 
and developed a complete line of modern enclosed arc 
lamps, alternating-current regulators, automatic trans- 
formers, switchboards and protecting devices. He has 
also engineered many important street lighting installa- 
tions, the most notable of which is the street lighting 
system in Cincinnati, O., which is remarkable in that 



2 MOTION PICTURE ELECTRICITY 

there are installed about 6,000 4-ampere series alternat- 
ing-current arc lamps which require over 105 separate 
circuits, with transformers, regulators and switchboards 
located in sub-stations. This is the largest arc lighting 
installation in the world using series alternating-current 
arc lamps. 

"In 1903 Mr. Hallberg was appointed general super- 
intendent and electrical engineer for the Cincinnati Gas 
& Electric Company, with full charge of its electric power 
stations and distribution system, comprising about 30,000 
horse-power of steam and electric equipment and a large 
storage battery. While in charge of this plant he made 
many important changes in the methods of operating the 
power plants and the storage battery, considerably reduc- 
ing losses and operating expenses. In the early part of 
1904, Mr. Hallberg was elected vice-chairman of the Cin- 
cinnati Chapter of the American Institute of Electrical 
Engineers, in which capacity he acted during that year. 

"In 1904 Mr. Hallberg established an office in New 
York City as consulting engineer. He has been retained 
as consulting and advisory engineer to the Commission 
on Municipal Electric Lighting of New York City, and 
has been appointed consulting expert for the National 
Carbon Company, Cleveland, O., in all matters relating 
to carbon for electrical purposes. He has also been re- 
tained as consulting engineer by several large lighting 
and power, industrial and manufacturing plants. 

"Mr. Hallberg is the author of numerous technical 
papers and articles. He is the inventor and patentee 
of electrical apparatus and systems, among which may 
be memtioned a single-phase to poly-phase alternating- 
current trunk line electric railway system. He is an 
associate member of the American Institute of Electrical 
Engineers, an associate member of the National Electric 
Light Association and a member of the Swedish En- 
gineers' Club of America." 

About six years ago, to bring the story down to date, 
Mr. Hallberg became interested in motion picture thea- 
ters through the granting to him of a patent on his electric 
"Economizer" and on naming arc lamps, special terminals 
and connections for use in picture houses. 



MOTION PICTURE ELECTRICITY 3 

Through his ability Mr. Hallberg has filled the position 
of consulting engineer for many large manufacturing 
establishments. Among these are the Atlantic Mills, of 
Providence, R. I.; A. D. Juilliard & Co., New York; 
National Carbon Company, Cleveland, O. ; Standard Silk 
Company, Phillipsburg, N. J.; Stanley G. I. Electric 
Manufacturing Company, Pittsfield, Mass. and Jacob 
Rupert Brewing Company, New York. 

He was selected by Horatio A. Foster, editor of "Fos- 
ter's Electrical Engineer's Pocket-Book" to write the 
chapter on "Arc Lamps and Arc Lighting" for that pub- 
lication, which is the guide and reference book consulted 
by all electrical engineers. It is also worthy of note that 
Mr. Hallberg has lectured frequently at the University 
of Columbia on electrical subjects. 



Foreword 



THE motion picture industry has within a very short 
time expanded to such tremendous proportions 
that the call for experienced managers and 
operators has been greater than the supply. Mechanics 
and electricians, in general, have qualified themselves as 
motion picture operators. There are, however, condi- 
tions to be met with in practice which require special 
knowledge in this particular line. 

In order, in a measure, to assist the operator in secur- 
ing education concerning the fundamental principles in- 
volved and the best methods of getting perfect results, 
the writer herewith presents a reproduction of his "Elec- 
trical Talks," which appeared in the Film Index some 
time ago. There is also included additional new matter 
and valuable data and tables which will be of interest to 
the proprietor, manager and operator of motion picture 
theaters. 

The day has passed when "any old thing goes." The 
public insists upon perfect pictures and perfect projec- 
tion, and it is incumbent upon each individual proprietor 
to meet this demand. The operator is the man behind 
the gun — he has to stand the brunt if the picture is not 
brilliant and if things don't go right generally, as far 
as the picture is concerned. He is the man whom I want 
to, and can assist, and a careful study of the following 
pages will make many operators better qualified to secure 
ideal results. 

I do not contend that there are not other ways to ac- 
complish results than those set forth within these pages, 
but I do claim that if these instructions are followed the 
best results will be obtained. 

Mr. Manager: You are conducting one of the most 
beneficial and educational institutions of the country. 



6 MOTION PICTURE ELECTRICITY 

Every motion picture theater, properly conducted, is, as 
I might say, a recreation and resting place for the over- 
worked brain and from an educational and amusement 
point of view it has no parallel because you teach without 
language through the eye to the brain by means of motion 
and acting, making everybody, foreigner or native, un- 
derstand alike. Therefore, you must do your part to 
make this transmission of intelligence without words as 
clear, easy and restful as possible by making your picture 
stand out bold, steady and clear on your screen. 



Publishers' Note 

Following a plan outlined a few years since, the pub- 
lishers of The Moving Picture World take pleasure in 
adding this volume to their standard publications for the 
moving picture industry. 

This book covers the very important end of the pic- 
ture theater electrical equipment. Its author is well known 
throughout the trade, and through his extensive ex- 
perience is particularly well equipped for the preparation 
of this volume. 

The publishers trust and believe the book will prove a 
valuable help. It contains complete, practical and tech- 
nical information which should answer the requirements 
of every reader, as well as standard tables of electrical 
and kindred subjects that are in constant use in the trade. 
We consider each department in this publication to be of 
the highest possible worth to those interested in motion 
picture exhibiting. Therefore, we highly recommend it 
as a technical authority. 

Chalmers Publishing Company 
July, -1914 



Technical Section 



MOTION PICTURE ELECTRICITY 9 

CHAPTER I 

Electricity 

THAT magnificent and most wonderful force or 
power, which almost runs the world, has in no little 
measure contributed to the phenomenal success of 
the motion picture industry. In justice to yourself, to 
your business and to your patrons, you must become 
more familiar with the functions and the general appli- 
cation of electricity in your theater so that you may 
economize and improve the results to the greatest pos- 
sible extent. 

There is no substitute, at the present moment at least, 
for the electric current as a means for advertising your 
place of business ; illuminating your theater and for pro- 
jecting brilliant pictures. 

The economical application and most practical selection 
of the many different kinds of current and appliances for 
motion picture theaters is not so thoroughly and gen- 
erally understood by the average electrician as one would 
believe. Experience in all branches of the electrical busi- 
ness, including designing and manufacturing electrical 
apparatus, electric wiring, installation of electrical ma- 
chines, ventilating systems and fittings of all kinds, gen- 
erating and distributing electric current, and last but not 
least, thorough knowledge of the requirements of motion 
picture theaters in particular, must be the accomplish- 
ments of your electrical advisor. 

The most difficult part of my problem will be to make 
everything clear and plain to you, but I am sure that if 
you will carefully read each line you will understand ; 
read it again and again so that you will remember it. 

Before discussing electrical equipment in detail, we 
will first become familiar with the meaning of electrical 
terms and names. 



10 MOTION PICTURE ELECTRICITY 

VOLTAGE 

Voltage is the word which signifies the pressure of the 
electric current on or in an electric circuit. 

Voltage is also represented by any of the following 
words which practically mean the same thing : Potential, 
Electro-Motive-Force, Electric Pressure. These are the 
most common. 

Voltage represents the pressure of an electric system 
or service just the same as pounds per square inch repre- 
sents the pressure in a water, steam or compressed air 
pipe. 

To give you a practical illustration by which you can 
judge voltage, I may say that an ordinary electric battery 
such as used for telegraph and fire alarm systems gives a 
pressure of just about one volt. Now if we take no 
such batteries and connect them in series one after the 
other, we will have between the first and the last wire 
a potential or voltage of no volts. 

Electric batteries which produce electric current by 
means of chemical action are not practical for heavy or 
continuous work, therefore, electric dynamos or gener- 
ators, which produce almost any desired voltage and 
current by the use of mechanical power to drive such 
generators are necessary and are universally used for the 
supply of current on a large scale. 

TESTING VOLTAGE 

Voltage is measured by a volt meter, which may be 
attached to the two wires to be tested. Another method 
of testing voltage roughly is to connect two incandescent 
lamps of the same candle power, each one of no volts, 
in series. If both lamps burn bright, that is, giving the 
normal candle power, you know that the circuit delivers 
about 220 volts. If the lamps burn very dim, giving only 
one-quarter of the normal candle power, the circuit de- 
livers about no volts. This method of testing with lamps 
is not recommended as being accurate or final, but may 



MOTION PICTURE ELECTRICITY 11 

be used by the traveling exhibitor in determining for 
himself before he connects his machine circuit, whether 
the no or 220 volt rheostat should be used. 

Suppose you have a water pipe one mile long and at 
the end of it there is a faucet and just ahead of the faucet 
a water pressure gauge is connected to the pipe, and the 
gauge indicates no pounds. Now open the faucet and 
you will see that the pressure gauge needle will fall back, 
depending upon the size of the pipe and bow wide you 
open the faucet. If the pipe is very small, the friction 
which the water creates in flowing against the wall of 
the pipe will cause the pressure at the end to drop very 
low. 

Just so is the voltage of a circuit affected. If you have 
two small wires running a distance of a mile and at the 
end of the wires we connect an arc lamp, a quantity of 
incandescent lamps, or a motor, the voltage, when the 
arc lamp is not burning, is no. When the load is 
switched on, the voltage may drop very low if the wires 
are not large enough, due to the friction or resistance 
offered by the wire to the flow of current; and it is evi- 
dent that the arc lamp, the incandescent lamps, or the 
motor at the end o>f your wires will not operate properly. 
I believe that the foregoing explanation will give you a 
good idea of the word or term voltage. 

AMPERE 

Ampere is the word which signifies the quantity or 
volume of electricity flowing through an electric circuit, 
arc lamp, incandescent lamp, motor or other machine, 
connected to the circuit. 

The measurement called "gallon" in the water system, 
or cubic foot for gas, designates quantity or volume. So 
does the ampere in the electric system. 

Remember, at the end of the water pipe referred to 
under the heading "Voltage," page 10, we had a pressure 
of no pounds on the gauge when no water was flowing 
and also at the end of the electric circuit we had no 
volts when the wires were not connected to the arc lamp, 



12 MOTION PICTURE ELECTRICITY 

or other load. The reason why the water gauge showed 
full no pounds or the volt meter no volts, at the end 
of the pipe line or the electric circuit, was that the faucet 
was closed or the electric wires were not connected to 
a load. There were no gallons of water flowing through 
the pipe and there were no amperes flowing through the 
electric wires, consequently no work was done and there 
simply remained the pressure at the end of the pipe or 
at the end of the wires ready to do work. 

As the diameter of the pipe has to be larger in order 
to carry more gallons of water, so does the electric wire 
have to be larger in order to carry more amperes. Other- 
wise the friction in the pipe or the resistance in the wire 
will use up the pressure or voltage before we get to the 
faucet or to the arc lamp, making the flow of gallons 
very low or the flow of amperes much less than it ought 
to be. From the above, you can make up your mind that : 

The size of the wire required for an electric cir- 
cuit depends entirely upon the number of amperes 
required for the electric installation. 

To give you an idea of the general amount or volume 
of an ampere I might tell you that one 16 c.p. carbon 
filament lamp on no volts requires about one-half am- 
pere; one regular enclosed arc lamp, such as are usually 
furnished by the electric lighting companies, requires 
about 5 amperes on no volts; one d. c. arc lamp for 
motion picture machine requires about 30 amperes. 

OHM 

Ohm is the word or electrical term which signifies the 
unit of resistance offered to the passage or transmis- 
sion of an electric current on or through an electric wire 
or conductor. 

The legal ohm is the resistance of a mercury 
column one square millimeter in cross sectional 
area and 106 centimeters in length. 

The ohm represents, in other words, "resistance" of 
electric conductors and machines and stands for the same 



MOTION PICTURE ELECTRICITY 13 

thing as the friction in a pipe carrying water, gas or air, 
In everyday discussion of electrical matters by the 
user of electrical machines, the word ohm is not em- 
ployed, but the word resistance being more common and 
easily understood is generally used. 

Under the heading "Voltage," page 10, we discovered 
that the voltage at the end of an electric circuit may be 
considerably lower than the voltage at the point where 
the current is generated and that the voltage drop was 
due to the flow of ampere through the circuit, in other 
words to the friction or resistance offered by the wire 
to the flow of current. The voltage was used up in push- 
ing the current through the wire just the same as water 
pressure is used up in pushing water through a pipe. 
When anything is moved from one point to another there 
is a loss depending upon the resistance offered. For in- 
stance, if you wish to move a ioo-pound weight from one 
point to another it induces a loss of power or energy de- 
pending upon the friction or resistance which, however, 
can be modified by using different means for reducing 
or increasing the friction. If the ioo-pound weight is 
set on a rough board it is difficult to move it because the 
rubbing of the weight against the board causes friction 
and the rougher the board the greater the friction and 
consequent power required to move the weight. This 
power is lost in the shape of heat, generated on the two 
rubbing of the weight against the board causes friction 
smooth less power would be required in moving the 
weight because the friction and consequently the heat loss 
is less. If we mount the weight on wheels or ball-bearings 
then much less power would be required in effecting the 
movement because the friction is then reduced to a min- 
imum. 

This example serves us very well in getting a clear 
understanding of resistance due to friction in moving 
anything from one point to another. Just so is the re- 
sistance or friction with consequent loss generating heat 
in electric wires and machines due to the resistance of- 
fered by the wire to the passage of the current, depend- 
ing upon; 



14 MOTION PICTURE ELECTRICITY 

(i) The size or diameter of the wire. 

(2) The material from which the wire is made. 

(3) The amount of current in amperes to be forced 
through the wire. 

We now understand that whenever resistance is in- 
troduced heat is generated and power is lost; therefore, 
we should reduce the resistance in all electric circuits 
and machines to the lowest possible amount in order to 
save electric. energy which costs money to produce. 

Copper is the material which for practical purposes 
offers the least resistance to the passage of electrical 
currents ; therefore copper is used for conducting wires 
and for all kinds of electrical machine windings. 

If we want to generate heat by means of electricity, 
then we introduce a wire made of some other material 
than copper, which offers greater resistance to the pass- 
age of electric current as is the case in electric heaters 
which are made of porcelain, with a wire made of nickel 
and copper, or nickel and steel, wound upon the porce- 
lain through which the current passes, thus heating the 
wire. 

If we wish to produce light with electricity, then for 
the incandescent or glow lamp there must be used a wire 
or conductor of very high resistance which glows yellow 
or white, depending upon the style of the lamp. 

If still more brilliant light is required it may be pro- 
duced by the electric arc between two metal or carbon 
points. In this case, the resistance is the air space be- 
tween the two points, which is so great that the current 
ordinarily used for electric lighting cannot jump across 
even the smallest air gap. In this case, the carbons must 
be put in actual contact before the "arc" can be started, 
and then the heat vaporizes the points which forms a gas, 
to take the place of the air, and this gas maintains the 
"arc" and permits the separation of the points forming 
what is ordinarly called an "arc light." 

In order to give you an idea of the comparative 
resistance of different kinds of materials, I will 
mention them in the following order from the 
lowest to the highest : Silver, copper, brass, zinc, 



MOTION PICTURE ELECTRICITY 15 

iron, nickel, carbon, plumbago, moist earth and 
water. 

You may be surprised to learn that if I take a copper 
rod one-half inch in diameter, 10 feet long and take a 
glass pipe one-half inch inside diameter, 10 feet long, 
filled with water, the resistance of the water in that pipe 
is to electricity 6,754 million times greater than the re- 
sistance of the copper rod. 

This may surprise some motion picture operators who 
have been using water for resistance in place of a rheo- 
stat, but it is nevertheless a fact that water cannot be 
used for a rheostat, unless something else, like salt, for 
instance, is put into the water in order to lower its re- 
sistance, as otherwise you could not force any current 
through the water rheostat. 

Operators who have used the earth as a resistance by 
driving pipes into the ground, or by putting metal plates 
on the bottom of a pond or lake, get a current through 
the moist earth and not through the water, unless the 
water is salt or is in some other way made a conductor. 

There are two kinds of resistance; one is due 
to the friction offered by the conductor, or wire, 
to the flow of the current which is usually called 
"Ohmic Resistance." 

The other kind of resistance is due to the mag- 
netic kick, or reaction, in an electric circuit or 
machine and is usually called "Inductive Resist- 
ance." 

While it is present with direct current systems it is 
not noticeable unless in special cases, but it is always 
a big factor when alternating current is used, and it is 
taken advantage of in several ways in order to do away 
with the rheostat for the control of arc lamps, as will 
be referred to later on. 

WATT 

Watt is the word which expresses the unit of electric 
power. One thousand watts are called one kilowatt and 
when one kilowatt is used for one hour a certain quan- 



16 MOTION PICTURE ELECTRICITY 

tity of power has been produced and used, which is called 
one "kilowatt hour." 

In order to abbreviate these terms kilowatt is written- 
and spoken of as k.w. and the kilowatt hour k.w.h. 

The kilowatt hour is the unit or measure by which 
electric power is made and sold, and this term is used 
all over the world. 

The watt .is the product or effect of voltage multiplied 
by amperes. For instance, if we have a circuit on which 
there is a voltage of ioo, and we operate a moving pic- 
ture arc lamp on direct current, taking 30 amperes, we 
multiply 100 by 30, which gives us 3,000 watts, which 
equals 3 kilowatts, or in abbreviated form 3 k.w. If we 
burn this arc lamp for one hour there will be consumed 
3 kilowatt hours, therefore if the rate is 10 cents per 
k.w.h. it would cost just 30 cents for one hour. 

If we burn this same arc lamp only one-half hour it 
is evident that the watt consumption will be just one-half 
or 1,500, which equals iy 2 k.w.h. and the bill for electric 
current will therefore also be one-half, or 15 cents. 

Electricity is different from all other powers or forces 
because it cannot be measured by volume, but only by its 
effect. 

When you buy water from the water company you get 
pressure as well as a certain number of gallons of water. 
The pressure may be used for driving a water motor or 
lifting a piston elevator and besides you have the original 
number of gallons of water left after the zvork has been 
done. 

When you buy electricity from the electric lighting 
company, you secure and pay for a certain effect which 
may be represented by power, heat or light, but after 
you have secured this effect you have nothing left. In 
other words there is no evidence of you having received 
anything but the work done on the instant. 

In order to give you a practical understanding of what 
you get when you purchase 1 k.w.h., I may say that 1 h.p. 
as usually applied to a steam engine equals exactly 746 
watts, or three-quarters of a k.w. If you operate a 1 h.p. 



MOTION PICTURE ELECTRICITY 17 

steam engine for one hour you have used I h.p. hour, and 
for an ordinary engine this would require about 10 pounds 
of coal. 

Now, if you substitute a I h.p. electric motor for the 
i h.p. steam engine the motor will require about 746 
watts, or three-quarter k.w.h. to do the same work, and 
the expense at the 10 cent rate would be just 7^2 cents 
for one hour's operation. 

I am giving you these examples in order that you may 
have it impressed upon your mind that electric power 
is in many respects similar to steam or water power and 
also to get you familiar with the comparative values of 
electricity. 

The ohm is the unit for measuring resistance 
in electric circuits and machines. 

Resistance is that property in a wire or other 
material which opposes a movement of any kind 
and is generally applied to represent the friction 
in an electric wire. The resistance should be kept 
as low as possible in order to reduce the heat loss 
and consequent expense for electric power use- 
lessly wasted. 

The kilowatt hour is the unit of measurement 
for electric power, and is the product of the volt- 
age multiplied by the amperes for all direct cur- 
rent systems. 

KILOWATT HOUR 

Before going into details as to how to figure kilowatt 
hours from voltage and amperes, I will give you further 
explanation. 

Suppose you hire a man capable of pumping sufficient 
water to fill a tank on your roof, and that it takes this 
man working with normal power and exertion ten hours 
to do the work, and you pay the man $1.50 or 15 cents 
per hour. At that rate you are paying 15 cents for each 
man hour. If you wanted to do this same work in one 
hour's time, you would have to put in ten pumps, employ 
ten men and at the rate of 15 cents per hour, the total ex- 



18 MOTION PICTURE ELECTRICITY 

pense would be just $1.50, but you would have the work 
done in just one-tenth of the time and the only extra 
expense to you would be the investment for the nine extra 
pumps, providing you could get the ten men just when 
you want them. 

It is generally agreed that one man power equals about 
one-eighth to one-fourth horse-power, depending upon 
the length of time the man is compelled to work. In 
other words, a man can produce about one-eighth horse- 
power continuously for ten hours. It is, of course, un- 
derstood that he may have to rest for a while, but no 
man can produce one-fourth horse-power continuously, 
only for a period of one-half hour, unless in exceptional 
cases. 

We have learned that one horse-power equals about 
three-fourths k.w., but allowing for all losses in the motor 
and the belt it takes about one k.w.h. to produce one 
horse-power. Therefore, one-eighth of a horse-power 
would require just one-eighth of a k.w., or 125 watts 
per hour. 

If we put an electric motor on the above mentioned 
pump, it would consume about 125 watts per hour, which 
for ten hours would be 1,250 watts or 1% k.w., which 
at the 10 cent rate would represent an expense for cur- 
rent of 123^ cents. This one-eighth horse-power motor 
would have to run steady for ten hours to do the work, 
and you understand, of course, that the electric light 
company would have to< furnish boiler, engine, dynamo, 
feed wires, transformer and meter large enough to drive 
this one-eighth horse-power motor and that the electric 
company would furnish you this quantity of power in 
ten hours' time, giving them a good, steady load at the 
expense to you of 12^ cents. 

Now, if you want to do this work in one hour, you 
would have to put in about i 1 /^ horse-power motor and 
you can readily understand that the electric light com- 
pany would have to put in much larger electric generat- 
ing equipment in order to supply you at the same 10 
cent rate for current, the income to the electric company 
would be just about 123/2 cents, but the expense would 



MOTION PICTURE ELECTRICITY 19 

be much greater because the company has to invest more 
money and run a bigger plant if you want your work 
done in one hour. 

That is the reason for the electric company in many 
places charging according to the number of hours you 
use your installation; therefore, when you put in your 
equipment you must do it in such a way that you have 
the smallest possible amount of installation or, as I might 
call it, "demand" on the electric company's service, in 
order to secure the lowest rate. The current saver for 
the motion picture machine lamp cuts your demand in 
half, not only cutting your old bill 50 per cent., but in 
some instances also reducing the rate, if the electric com- 
pany has a rate on the sliding scale, as many of them 
have. 

We all know that it costs more to put up a building 
in two months than to put it up in six months, because 
rush work means more expense in every way, and I want 
to impress this on your mind, because in laying out the 
electric equipment for theaters, considerable reduction 
can be made in the current consumption as well as in the 
rate, especially if the company has a sliding scale of rates. 
I have deemed it advisable to give you the foregoing 
example, because you must realize and understand these 
fundamental principles, and any time you spend at fa- 
miliarizing yourself with the illustrations given will save 
you a great deal of misunderstanding and expense and 
it will also give you a clear idea of why the electric light 
company charges different rates for different classes of 
service. 

As a comparison and standard of values, I will say 
that: 

One 16 c.p. carbon filament lamp takes about 50 watts 
per hour. 

One regular enclosed arc lamp takes about 500 watts 
per hour. 

One 4,000 c.p. flaming arc lamp takes about 50G watts 
per hour. 

One 12-inch fan motor takes about 50 watts per hour. 



20 MOTION PICTURE ELECTRICITY 

One 16-inch fan motor takes about ioo watts per hour. 
One ceiling fan takes about 125 watts. 
One 18-inch exhaust fan takes about 250 watts per 
hour. 

One 24-inch exhaust fan takes about 400 watts per 
hour. 

One 36-inch exhaust fan takes about 1,000 watts per 
hour, or 1 k.w. 

One ordinary moving picture lamp on direct current 
with rheostat on no volts takes about 3,300 watts per 
hour, or 3 3-10 k.w. This same moving picture lamp 
on 220 volts takes 6,600 watts or 6 6-10 k.w. per hour. 

One moving picture lamp with rheostat on alternating 
current no volt circuit takes 4,500 watts or 4 5-10 k.w. 
per hour. This same lamp on 220 volts takes 9,000 
watts, or 9 k.w. per hour. 

Keeping this data in mind, you can easily figure for 
yourself how many watts or k.w. your installation re- 
quires. 

FORMULAS 

For the electrician and operator as well as the man- 
ager or proprietor who may be interested, the following 
data and formulas are of great value in figuring voltage, 
amperes, resistance and watts. 

Formula No. 1 

E 



C = 



R 



Formula No. 1 is the electrical designation for figur- 
ing the number of amperes which will pass through a 
rheostat when you know the voltage and the number of 
ohms of your rheostat. For instance, if you have a line 
voltage of 100 and your rheostat has a resistance of 5 
ohms and you want to find out how many amperes will 



MOTION PICTURE ELECTRICITY 21 

pass through the rheostat, the formula extended in sim- 
plified form will read : 

100 volts 

Amperes equals , or, written out: ioo 

5 ohms 
volts divided by 5 ohms equals 20 amperes, and this is 
the amount of current you would get through your rheo- 
stat, which would, in that case, be nothing more than an 
electric heater taking 20 amperes from the 100 volt line. 

Formula No. 2 

E 

R = 

C 
Formula No. 2 is the electrical designation for figur- 
ing the number of ohms for resistance required in your 
rheostat when you know the line voltage and the number 
of amperes required for your work. For instance, if you 
have 100 volts and you require 20 amperes for your work, 
the formula in simplified form reads as follows : 

100 volts 

Resistance in ohms of rheostat equals , 

20 amperes 
or written out: 100 volts divided by 20 amperes equals 
5 ohms, which is the resistance required in your rheostat. 

Formula No. 3 

E = CxR 

Formula No. 3 is the electrical designation for figur- 
ing the number of volts required to force a certain num- 
ber 'of amperes through a rheostat of given resistance. 
For instance, if you have a flow of 20 amperes through 
a rheostat offering a resistance of 5 ohms, the formula 
in simplified form reads as follows : 

Voltage equals 20 amperes x 5 ohms, or written out : 
20 amperes times 5 ohms equals 100 volts. In other 
words, it would take just 100 volts to force 20 amperes 
through a rheostat having a resistance of 5 ohms. 



22 MOTION PICTURE ELECTRICITY 

Formula No. 4 

W=CxE 
Formula No. 4 is the electrical designation for figur- 
ing the number of watts which will be delivered by a 
given voltage and flow of amperes on a D. C. and for 
A. C. where the load is made up of only "ohmic" resist- 
ance. It cannot be used correctly for A. C. where motors, 
arc lamps and current savers are used, as such a load 
has in addition to "ohmic" resistance what is called "in- 
ductive" resistance. For instance, if you have on D. C. 
system a flow of 20 amperes and the voltage is 100, the 
formula in simplified form reads as follows: 

100 volts x 20 amperes equals 2,000 watts. In view 
of the last formula, you can easily remember that 

For all D. C. systems it is only necessary to mul- 
tiply the line voltage by the amperes flowing 
through the circuit in order to find the number of 
watts required. 

In explanation of these formulas remember the fol- 
lowing: 

C stands for current in amperes. 
E stands for the line voltage or the voltage at the 
point where test is made. 

R stands for resistance, of the rheostat or machine, 
in ohms. 

W stands for watts. 

The amperes flowing through a circuit or ma- 
chine are equal to the voltage, divided by the 
resistance in ohms. 

The resistance in ohms of a circuit or machine 
is equal to the voltage divided by the amperes 
flowing. 

The voltage at the terminals of a circuit or 
machine is equal to current in amperes flowing 
multiplied by the resistance in ohms. 

The watts consumed in a circuit, machine, in- 
candescent or arc lamps are equal to the current 
in amperes times the voltage at the terminals 
where the test is made excepting for alternating 
systems with "inductive" loads. 



MOTION PICTURE ELECTRICITY 



23 



T 



CHAPTER II 

Generation of Current 

HERE are two kinds of electric current used for 
practical purposes, which may be designated as 
follows : 



(i) Direct current. 

(2) Alternating current. 

Either one of which may be used for electric lighting, 
heat and power. 




DIRECT CURRENT 

Direct current, also called continuous current, flows 
in one direction only and has al- 
ways two fixed poles, one called 
"Positive," designated by ( + ), 
the other "Negative," designated 
by (-). 

Direct current may be produced 
in several ways, the most common 
by means of the electric battery, 
which through the action of acid 
on metals produces electricity in 
small quantity suitable for tele- 
phones, medical batteries, fire 
alarm systems, door bells, etc., or 
by means of an electric dynamo or 
generator driven by a steam en- 
gine or other power, as is the prac- 
tice in the regular electric power 
stations. 

Fig. 1 illustrates an ordinary 

electric battery usually composed 

of a glass jar in which is placed 

two metal elements like zinc and 

Fig- 1 copper, for instance, and the jar 



ACID 






24 



MOTION PICTURE ELECTRICITY 



is then partly filled with a fluid composed of sulphuric 
acid and water in some cases. The action of the acid 
upon the zinc causes a chemical change to take place, 
which generates a current flowing from the zinc to the 
copper, but at the upper end of the electric element or 
electrodes the current flows from the copper to the zinc, 
making the copper the positive terminal. 

There are many other forms of batteries, for instance 
the one used for electric bells, in which the elements are 
made of zinc and carbon with a solution of salamoniac 
surrounding the elements. You are undoubtedly ac- 
quainted with this form of battery, as it is extensively 
used for door bells, etc. 

As already stated, where a large quantity of power is 
required the chemical method is not practical, therefore 
a power plant like that illustrated in Fig. 2 is substituted. 




Fig. 2 



An electric power plant is usually composed of four 
distinct parts : 

(1) The boiler. 

(2) The steam engine. 

(3) The dynamo or electri generator. 

(4) The switchboard. 

The illustration shows in a simple way such an instal- 
lation without the switchboard. 

The D. C. electric generator produces electricity by re- 
volving its armature at high speed under the influence of 



MOTION PICTURE ELECTRICITY 25 

the magnetism in the stationary magnetic pole pieces or 
"field," as it is usually called. 

Electric generators are now made in all sizes, from 
the smallest up to 10,000 k.w., these large ones requir- 
ing engines approximating 20,000 h.p. 

From the generator the current is brought through 
large copper conductors to a switchboard in the power 
station, where it is distributed over as many switches as 
required to circuits running to different parts of the 
town or city. 

Upon the switchboard, which is usually made of mar- 
ble, there are mounted protective fuses or automatic cir- 
cuit breakers, switches, volt meter and one or more 
ampere meters. There is also included a field rheostat 
for each generator by means of which the voltage may 
be increased at the power house when the load is heavy 
in order to overcome the losses of voltage-drop in the 
feed wires, or to lower the voltage when the load is light, 
in order to maintain it as constant as possible at the 
theater or other place where the current is used. 

Fig. 3 gives a diagrammatical illustration of an elec- 
tric generator and a 2-wire distribution system in its sim- 
plest form operating a motor, incandescent lamps and 
arc lamps. The illustration indicates the names of the 
principal parts of the system and how connections are 
made. 

We have already learned that the further the current 
has to be transmitted, the greater the drop of voltage in 
the wires, therefore it takes larger wires to carry a given 
quantity of amperes a long distance, and this is also one 
of the reasons why the field rheostat for the generator is 
necessary at the power house in order to raise the voltage 
of the generator to overcome the line losses, and it is one 
of the duties of the dynamo attendant to keep the voltage 
at the proper amount at all times by means of the field 
rheostat. 

The battery is only suitable for small and inter- 
mittent work. 



26 



MOTION PICTURE ELECTRICITY 



DIRECT CURRENT 

2 WIRE ELECTRIC 

SYSTEM 



RHEOSTAT 



SHUNT 
FIELD WINDING 



"\ ^ARMATURE 

— COMMUTATOR 



BRUSHES 




Fig- 3 



MOTION PICTURE ELECTRICITY 27 

Where large current supply is required, it be- 
comes necessary to make the electricity by a dyna- 
mo electric machine driven by an engine or similar 
power. 

THREE-WIRE SYSTEM FOR DIRECT 
CURRENT 

The 2-wire direct current distributing system is used, 
as a general rule, in small plants and in isolated plants 
where the distance from the electric generator to the 
point where the current is used is not very great. In a 
building, for instance, the distance would never be over 
a few hundred feet, and in a small town the distance from 
the power .station to the furthest consumer might not be 
over one mile. In such places the 2-wire system may be 
installed and used, although the cost for copper wire is 
great as compared with the 3-wire system, which is gen- 
erally used where a large amount of power is required 
and where the distance may be several miles, as is the 
case in the larger towns and cities. 

The 2-wire system may be either no or 220 volts, but 
only one of these voltages can be obtained from a 2-wire 
system, and it is a well-known fact that for electric light- 
ing, no volts is more suitable than 220 volts, but where 
there are a large number of motors and where the dis- 
tance is great the 3-wire 220-volt system may have to be 
installed in order to cut down the expense of copper wire 
between the power house and the place where the current 
is used. 

In order to make a more economical and flexible in- 
stallation, the 3-wire system is installed, which enables 
the electric company to transmit the power for motors 
and lighting on the same wires at half the expense for 
copper, and, at the same time, to give you no as well as 
220-volt current. 

Fig. 4 illustrates in simplified form the 3-wire system. 
There are two dynamos or electric generators, A and B, 
which are connected in series. Both are driven from the 



28 



MOTION PICTURE ELECTRICITY 



D.C. 3 WIRE SYSTEM 
110 V. DYNAMO 110 V. DYNAMO 




^ 



*r 



INCANDESCENT 
LAMPS 



■* 



■K- 



r^ 110V - 

{J ) MOTOR 



220 V. 
MOTOR 




./V 



110 V M.P. LAMP 



/ 




V. M.P. LAMP 



Fig. 4 



MOTION PICTURE ELECTRICITY 29 

same source of power, and each one may be made to gen- 
erate no volts. You will observe that there are three 
line wires with this system and that while each generator 
gives only no volts, by being connected in series it is 
possible also to get 220 volts from the same system. 

Considering generator A, you observe the current 
leaves the positive terminal indicated by (+), traveling 
on the left-hand outside wire to the lamp or motor, 
through the same and back over the middle wire to the 
negative terminal of the generator, thus completing the 
circuit and lighting the lamp or operating the motor. 

The same performance takes place on generator B, the 
current leaving the positive terminal, but in this case 
going out over the middle wire through the lamp and re- 
turns over the outside right-hand wire to the negative 
terminal of the generator. 

It is evident that if we want to maintain the same load 
on each dynamo, it becomes necessary to balance the load 
so that there will be just as many amperes taken from one 
side as the other on this 3-wire system. 

In practice this is rather difficult to do in some instances, 
especially where large arc lamps or motors are used, un- 
less the arc lamps and motors are made for 220 volts so 
as to operate on the two outside wires, and it is the 
tendency of the electric lighting companies to make you 
connect all motors one h.p. and larger, and all arc lamps 
taking more than 10 amperes on the two outside or 220- 
volt wires of the 3-wire system, which would otherwise 
be unbalanced, and would throw more load on one gen- 
erator than on the other, which should be obviated be- 
cause it inclines to lower the voltage on the side of the 
3-wire system, which has to carry the greatest load. This 
drop in voltage on one side of the system is especially no- 
ticeable with motion picture arc lamps, because they re- 
quire from 25 to 30 amperes, and draw more than this 
amount of current from the wire at the instant the carbons 
are put together in order to strike the arc, and you may 
have noticed that when the motion picture lamp is started, 
there is a considerable drop in the candle-power of the 
incandescent lamps connected to the same side of the sys- 



50 MOTION PICTURE ELECTRICITY 

tern, whereas the lamps on the other side will increase in 
candle-power, due to the voltage going down on one side 
and up on the other. 

This drop in voltage on one side of the unbalanced 
3-wire system is partly due to slipping of the belt on the 
generator, which supplies the loaded side, and also due 
to the drop in voltage in the generator and wires supply- 
ing that side of the system. 

It is obvious that if the moving picture lamp or motor 
is connected to the outside or 220-volt wires, there is no 
such disturbance or unbalancing of the 3-wire system, and 
that is the main reason for the electric lighting company 
insisting upon having all motion picture arc lamps con- 
nected to the 220-volt wires, as they may receive com- 
plaints from your neighbors who are fed from the same 
wires and whose lamps go up and down in candle-power 
every time the moving-picture lamp is switched on or off. 

You are to understand, of course, that if the load is 
very light, consisting of only a few incandescent lamps, 
fan motors or small 5-ampere enclosed arc lamps, this un- 
balancing does not make so much difference, but with 
large motors, and especially with moving-picture arc 
lamps, the disturbance on a 3-wire system if operated on 
one side or on no volts is very great and undesirable. 
By observing the diagram, you will see by the arrows in 
which direction the current flows, and it is evident that 
when there are exactly the same number of amperes used 
on either side of the 3-wire system, the current goes en- 
tirely from the outside left to the outside right-hand wire, 
there being no current flowing over the middle or, as it is 
called, "neutral" wire. 

If, however, there is required ten amperes on one side 
and only five amperes on the other side of the 3-wire 
system, there will be five amperes flowing from outside 
wire to outside wire, and five amperes more will flow on 
one outside wire and on the neutral wire. 

The early electrical systems were all of the direct cur- 
rent type, and so many motors, arc lamps and machines 
are in service that the electric lighting companies are 
obliged to continue supplying them with direct current, 



MOTION PICTURE ELECTRICITY 31 

especially in the manufacturing and business sections of 
the larger cities, where the distance is not great ; but the 
tendency is to change, as far as possible, to the alternating 
current system of distribution, which is more economical 
where long distance is considered. For this reason in the 
outskirts of the larger towns and cities it is not unusual to 
find alternating current only, whereas in the center of the 
city the system is direct current. The more modern plants 
are all of the alternating type even in the smallest towns, 
but either system has advantages of its own. 

The direct current system is, as a general rule, low 
voltage, both outside and inside of the building, and is 
therefore practically harmless, and for certain classes of 
work, such as small motors and arc lamps, the direct 
current has the advantage over the alternating in some 
respects. 

The 3-wire direct current system is generally 
supplied by two separate generators connected in 
series. 

The current is distributed over three wires, the 
middle one of which is called the "neutral." 

It is essential that on a 3-wire system the load in 
amperes on either side be kept the same, or as 
nearly so as possible. 

If a 3-wire system has to supply a greater num- 
ber of amperes on one side than on the other, the 
side with the greatest load will supply a lower 
voltage than the other side. 

ALTERNATING CURRENT 

You have been advised that direct current flows in one 
direction, and is therefore also called "continuous cur- 
rent," in other words, it flows out over one wire through 
the lamp or motor, back to the dynamo over the second 
wire, thus completing the circuit. 

Alternating current derives its name from the fact that 
it alternates, that is, it goes back and forth between the 
dynamo and the lamp or motor, making a complete re- 
versal of the current many times per second, depending 



62 



MOTION PICTURE ELECTRICITY 



— A" 



upon what is called the "frequency," also called the 

"cycles" of the circuit. 

In order to make this matter more clear, your attention 

is called to Fig. 5, which illustrates a water power system. 

Referring to the illustration : A is an elevated water tank, 

B is a receiving or storage water tank, C is a pump, G is 

a water motor. They are all connected by pipes D, E, F 

andH. 

Suppose we start pump C 
lifting the water from the 
lower tank through pipes D and 
E, filling upper tank A. There 
will be created a water pressure 
through pipe F at the motor G. 
If the starting valve on the 
motor is open, the water will 
cause the motor to rotate, dis- 
charging through pipe H into 
the lower tank, thus completing 
the continuous flow of water, 
which it takes power to create 
through the pump C and which 
is available at another point 
through the water motor G. 
This is a good representation of 
the direct current electric gen- 
erating system, in which the 
pump C and the tank A would 
represent the electric genera- 
tor and the water motor G, the 
electric motor. 

Fig. 6 illustrates another type 
of water system in which the 
flow of water is not continuous. 
Referring to the illustration: 
A is the cylinder of an engine 
having a piston — D, which can 
exert movement of a crank, 
shaft and flywheel through the 
piston rod K. The cylinder A 
is connected by two pipes E and 




MOTION PICTURE ELECTRICITY 



33 



F, with another similar pump, cylinder B having a piston 
C, connected with a piston rod. The operation of this 
water system is as follows : 

By moving the piston rod and consequently the piston 
C towards J, that is, by pulling it out as if it were con- 
nected to a crank, the water J will be compressed and 
forced up through the pipe F into cylinder A on the side 
indicated by I, creating a pressure on motor piston D 
which will, through piston rod K, start the engine back- 
wards. When the piston C has been pulled out to a stop, 





A 








iiiiiiiiiniii 


u 


lllllllliilll 


111 K 




llllilillillillll 


II 

r 




! 


[ o 




















I 








N 


F 
















b/> 


« 




(i 




■■mm 




■minim 


i 


— «y 




Fig. 6 



the water pressure will cease and engine A would stop, 
but its fly-wheel will carry the crank over the center as 
it would in any kind of an engine. 

If we now push the piston C backwards towards G, the 
pressure will force the water up through pipe E into the 



34 MOTION PICTURE ELECTRICITY 

chamber — pushing the piston D and piston rod K towards 
I — completing the backward motion of the crank, shaft 
and fly-wheel of the motor A. It is evident that by mov- 
ing the piston in the cylinder B back and forth the fly- 
wheel of the motor A can be kept in continuous motion, 
as the water pressure changes alternately from side I to 
side H of motor piston D and vice-versa. 

Here we have the simplest form of an alternating cur- 
rent water system in which the pump B is the dynamo as 
compared with an electric system ; pipes E and F are the 
wires and A is the alternating current motor. The process 
of operation is extremely simple, and the illustrations can 
be easily understood by reference to the above description 
and illustration. 

Anyone can understand that in Fig. 5 the operation is 
continuous in one direction being very smooth without 
interruption and the water motor turns around without 
oscillating motion and can never stop on a dead center. 

With the alternating water system in Fig. 6, however, 
the movement of the piston in the water motor A is oscil- 
lating and the motor cannot be started if the piston is at 
either one of the extreme ends of the cylinder A. In 
other words, we have as on any ordinary single cylinder 
engine, two dead centers, indicated at L and M in Fig. 6. 

The alternating current single phase system has exactly 
the same effect on a motor. It has a dead center on which 
it is impossible to start the motor unless first revolved by 
hand or by other means for inducing the starting of the 
rotating member of the motor are introduced. 

Having established in our mind the fact that an alter- 
nating current has one or more dead centers or periods 
when no power is generated or delivered at the instant 
the current is being reversed, we come to the conclusion 
that an alternating current is the kind which surges back 
and forth through the circuit, and while the voltage may 
be no, or any other number of volts at a given instant, 
there are other moments at which time there is absolutely 
no voltage on the system. It is of course necessary to 
make these reversals of the current so frequent that, 
when the current has to be used for electric lighting, 



MOTION PICTURE ELECTRICITY 35 

there will be no serious interference with the continuity 
of the light which is more difficult with arc lamps than 
with incandescent lamps. 

The alternating current is so named because it 
oscillates or reverses, in other words goes back 
and forth over the same wires and through the 
same lamps and motors many times a second. 

The alternating current may be of any given 
voltage, but this voltage is only apparent because 
at the instant of each reversal of the current there 
is no voltage generated. 

Due to the fact that there are moments of no 
voltage on an alternating system, it is necessary to 
make the frequency or change of reversal many 
times per second in order to maintain the illumina- 
tion constant. 

In order to clearly impress upon your mind the differ- 
ence between direct and alternating current, I would like 
to offer one more example : 

The Mississippi river gathers the water in the upper 
part of the country, flowing continuously towards the 
gulf ; the water has a steady, direct flow practically from 
north to south. A large water-wheel may be set in the 
river and due to the downward flow of the water it would 
rotate and produce power. The sun gathers the water 
from the gulf to the clouds, and the clouds carry the 
water back again into the upper part of the country from 
whence it flows; the river thus completing this direct or 
continuous current water flow. 

The lower part of the Hudson river, on the other hand, 
is a good representation of the alternating current sys- 
tem, because when the tide is low the fresh water flows 
downward towards the ocean. Within a few hours when 
the tide rises again, the water flows in the opposite direc- 
tion against the downward stream of water — actually re- 
versing it. This is an alternating current water system ; 
surging back and forth with the rise and fall of the tide 
and the cycle of reversal of this current is equal to the rise 
and fall of the tide. If a large water-wheel should be 



36 



MOTION PICTURE ELECTRICITY 



put in the Hudson river it would turn in one direction 
when the tide is ebbing; it would then stop for a short 
time and when the tide begins to rise the water-wheel 
would be turned in the opposite direction. 

This analogy shows you in the simplest possible way 
how an alternating current, whether represented by water 
or electricity, actually stands still or rather is inactive at 
the instant the flow of the current is being reversed; in 
other words., there is no current, no pressure or no voltage 
at the instant of current reversal. 

Fig. 3 shows a direct-current electric generator having 
an iron core terminating into two pole pieces called the 
"field" surrounding part of the rotating armature. There 



+ 




Fig. 7 



is also a device mounted on the armature shaft and con- 
nected to the armature windings called the "commutator" 
and there are also two or more brushes which collect the 
current generated by the armature through the commu- 



MOTION PICTURE ELECTRICITY 



37 



tator. Practically all direct current generators must be 
equipped with a commutator, the purpose of which is to 
keep the current flow in one direction. 

An alternating current generator does not require a 
commutator, and is therefore much simpler in construc- 
tion and, furthermore, as the commutator can be dis- 
pensed with, it is possible to generate a much higher volt- 
age and there is absolutely no chance of sparking. 

Fig. 7 illustrates a simple form of the alternating cur- 
rent generator. The rotating magnet is mounted on a 
shaft which, by means of a pulley and belt, is rotated at 
high speed between the upper and lower iron cores. 
These iron cores are surrounded by coils of copper wire 
which may be connected to the line wires. Suppose the 
magnet is rotating under the upper iron core in Fig. 7; 

N 





Fig. 8 



S 
Fig. 9 



the iron core will be magnetized to the fullest extent, 
making the lower end of it a north pole magnet and the 
upper end a south pole, as indicated by "S." At the in- 
stant the rotating south pole "S" is directly over the lower 
stationary iron core it will be magnetized to the fullest 
extent south and north as indicated by a S" and "N." As 
we continue to revolve the magnet we will stop at the 
position indicated in Fig. 8. At this instant the rotating 
magnet is exerting no influence on either one of the iron 
cores. 

Continuing the movement of the magnet, we find, as 
illustrated in Fig. 9, that the magnetism in the upper 



38 



MOTION PICTURE ELECTRICITY 




Fig. 10 



and lower iron core has been reversed. Going still fur- 
ther, as indicated in Fig. 10, there is again a point or 
instant when there is no magnetism in the upper and 
lower iron cores. 

It may be well to impress 
upon you the fact that when 
you rotate or move a magnet 
towards or from a piece of 
soft iron, or in fact any kind 
of iron, the iron will remain 
magnetized as long as it is un- 
der the influence of the mag- 
net, which in the case illus- 
trated is rotating between two 
soft iron cores. 

I want to further impress 
upon you that when a coil 
of copper wire is put on a bar or core of soft iron, electric 
current can be induced or created in the copper coil by 
suddenly moving a magnet past the end of the soft iron 
core upon which the coil is mounted. 

It is also a fact that if you move the north pole of a 
magnet past a soft iron core surrounded by a copper wire 
coil, electricity will be generated in the coil flowing in 
one direction and if you move this same north pole back 
and forth the current will be pulsating, but it will always 
be in the same direction. 

Suppose we influence this same core and coil by first 
moving a north pole magnet past it ; the current will flow 
in one direction. Instead of coming back with the north 
pole magnet we bring around the south pole, then the 
magnetism in the soft iron core will be reversed and a 
current will be generated in the coil, but flowing in the 
opposite direction. 

As it is always easier to secure a rotating motion, 
dynamos or electric generators for alternating current 
have the magnet pole pieces mounted on a shaft, and the 
soft iron cores and the copper wire magnet coils are 
mounted on a frame surrounding the rotating magnet 



MOTION PICTURE ELECTRICITY 39 

pole pieces. This arrangement permits sudden and 
smooth movement of the rotating magnet past the sta- 
tionary iron cores which are thereby first magnetized in 
one direction then in the other as fast as the magnet pole 
pieces are being rotated, and in consequence thereof elec- 
tric current is generated in the copper wire coils which is 
then distributed to the line wires. 

It is obvious that the magnetism will be strenuous in 
the iron cores and the current on the line will conse- 
quently be at the highest voltage or strength when the 
rotating magnet is in the position indicated in Figs. 
7 and 9. 

It is also evident that when the rotating magnet is in 
the position indicated in Figs. 8 and 10, there is no volt- 
age or current on the line, because at that instant there 
is no magnetism in the soft iron cores, but the moment 
the rotating magnet is turned slightly, each one of the 
two poles is nearing its respective stationary iron core, 
which is thereby magnetized and begins to generate cur- 
rent in the copper magnet coil. 

To give an illustration of the flow of current we might 
assume that when the magnet is in the position shown 
in Fig. 7 the upper line wire is positive ( + ) and the 
lower is negative ( — ), but when the magnet is in the 
position as shown in Fig. 9 the upper line wire becomes 
negative and the lower one positive, and the continued 
motion of the rotating magnet changes the direction of 
the flow of the current as many times per minute as the 
pole piece is rotated past the iron core. 

Electric current can be reduced in a coil of copper 
wire surrounding a soft iron core by suddenly mov- 
ing the pole of a magnet past the iron core. The 
direction of the flow of the current in a coil sur- 
rounding a soft iron core depends upon which pole 
of a magnet is moved past the core. 

By rotating a magnet past a soft iron core 
surrounded bv copper wire, successive impulses of 
current are produced. 

The frequency of the reversals depends upon 



40 



MOTION PICTURE ELECTRICITY 



the speed at which the magnet poles are rotated 
past the soft iron core. 

CYCLES 



By modification of the number of rotating magnet 
poles, and the speed at which they are rotated, almost any 
desired frequency or number of alternations may be 
obtained. 

It is possible by means of a simple diagram, or curve, 
to give a representation of the alternating current and 




Fig. ii 

your attention is called to Fig. n, in which the horizontal 
line represents time; the curves above the line represent 
positive current generated, and the curves below the line 
represent negative current. The vertical line on the left 
is a scale of amperes running from zero to 40 above the 
horizontal line for positive current and below the line for 
negative current. 

Suppose in Fig. 11 the distance from o to f represents 
one-twentieth of a second. Assume also that we have a 
60-cycle alternating current circuit, which would supply 
a load of 30 amperes. Now we will close the switch at 
the instant the current is at zero. Following the curve 
we find the current jumps from zero up to 30 amperes, 
positive current ; then drops to a, continuing down- 
ward ; then negative to 30 amperes through b ; up posi- 
tive ; down through c negative ; up through d positive ; 
down through e negative to f. Here we have in one- 
twentieth of a second made three cycles, or complete re- 
versals, and you will note that there have been three posi- 



MOTION PICTURE ELECTRICITY 41 

tive impulses of 30 amperes each and three negative im- 
pulses of 30 amperes alternately following each other. 
Also you cannot fail to observe that at the points o, a, b, 
c, d, e and f, there is absolutely no current generated; 
neither voltage nor amperes, because at that instant the 
current changes from one direction to the other. 

If we had drawn the time line twenty times longer we 
would have shown just exactly what happens in a 60-cycle 
circuit during the period of one second. It would have 
shown 60 positive impulses and 60 of the negative. 

Wherever the curve strikes the horizontal time line, 
at that instant there is no voltage or current generated, 
therefore those points represent dead centers, as one 
might call them, and at those instants if a light is burn- 
ing it is actually out, but owing to the red hot filament 
which carries the current, or to the heated carbons of 
an arc lamp and the vapor of the arc, the glow is main- 
tained, providing the frequency of the current or the 
number of cycles is sufficiently great to make the change 
undetectable by the eye. 

By this you can understand that the more impulses 
the current makes in the period of a second the steadier 
the light will be. That is one reason why with 133 cycles 
(16,000 alternations) an arc light appears to burn with 
a steadier glow than at 60 cycles (7,200 alternations) 
and still more steady than at 30 cycles (3,600 alterna- 
tions). 

It is a fact that it is very difficult to operate arc lamps 
on circuits of 25 and 30 cycles, because this frequency 
is very low and the interruptions are quite noticeable to 
the eye, especially on 25 cycles. 

Some years ago, those now interested in the electrical 
business did not use the terms "frequency and cycles," 
but the word "alternations" was used to express the rapid- 
ity at which the alternating current changed. For in- 
stance, in the early days almost all systems were made 
to deliver 16,000 alternations per minute. Later the sys- 
tems became 7,200 alternations per minute, and a few 
power systems were introduced operating at 3,600 alter- 
nations per minute. 

On account of the many figures representing the num- 



42 



MOTION PICTURE ELECTRICITY 



ber of changes in a minute and the comparatively long 
space of time of a minute, the electrical profession had, 
for a long time, used the term "cycle" representing one 
complete reversal of the current or one positive and one 
negative impulse. If this occurred 60 times in one sec- 
ond, the circuit was said to deliver a frequency of 60 
cycles per second. 

I now call your attention to 
Fig. 12, which represents a cop- 
per coil surrounding a soft iron 
core. This core is under the in- 
fluence of a rotating magnet with 
one north and one south pole. 
The core is revolved by a belt or 
other means at high speed. Sup- 
pose the magnet poles N and S 
are revolved at a speed of 3,600 
revolutions per minute, there be- 
ing two poles, one north and one 
south. Then the number of al- 
ternations during one minute will be equal to 3,600 multi- 
plied by 2 or 7,200 alternations per minute, which would 
be correct for the current delivered to the line. 

Suppose, in Fig. 12, that instead of driving the magnet 
at a speed of 3,600 revolutions it be turned only 1,800 
revolutions per minute; then the number of alternations 
would be 1,800 times 2 or 3,600 alternations per minute. 

Let us take 7,200 alternations per minute and reduce 
this to cycles ; first divide 7,200 by 2, which would equal 
3,600 ; then divide this amount by 60 seconds, which gives 
60 — representing the number of cycles per second. 




ALTERNATIONS 



To figure the number of alternations delivered 
per minute by an electric generator, multiply the 
number of magnet poles on the generator by the 
speed in revolutions per minute. 



MOTION PICTURE ELECTRICITY 43 

CYCLES PER SECOND 

When the number of alternations per minute is 
known, the cycles may be determined by dividing 
___ the number of alternations by 2, then dividing the 
amount obtained by 60. 

The alternating current generator is an electric 
machine in which, by the magnetism from rotating 
pole pieces, currents are induced in copper coils, 
surrounding soft iron cores influenced by the ro- 
tating magnet poles. 

An alternating current electric generator can 
be made to deliver a certain number of cycles per 
second with a given number of rotating magnet 
poles at a fixed speed. If the speed is doubled, the 
number of cycles per second is also doubled. The 
number of cycles may also be doubled by increas- 
ing the number of rotating poles to twice the num- 
ber, or the same frequency may be obtained by 
doubling the number of poles and cutting the speed 
in two. 

THE A. C. GENERATOR 

- Assuming that you have formed a clear idea of how 
alternating current is generated in a copper coil sur- 
rounding a soft iron core under the influence of a rotat- 
ing magnet, I will next call your attention to Fig. 13, 
which is a diagrammatic representation of an alternating 
current electric generator. The machine is mounted on 
a base and is composed of a magnet frame, usually made 
of cast iron, within which are clamped iron cores made 
of thin sheets of soft iron or special magnetic steel. This 
soft iron core is so made that copper wire coils can be 
mounted on projections forming soft iron core pole pieces 
which do not hold or maintain any magnetism except at 
the instant one of the rotating magnet poles passes by it. 

Upon' a main shaft is mounted a pulley and two or more 
magnet poles which are always magnetically charged 
when the machine is to generate current. 

By means of a pulley or direct connection to an engine 



44 



MOTION PICTURE ELECTRICITY 



or other source of power, the shaft and the magnet poles 
are rotated at high speed acting magnetically upon the 
stationary soft iron cores, transmitting alternately north 
and south pole magnetism to the cores, thereby inducing 
a current to flow in the copper wire coils, which are con- 
nected to the terminals at the top of the generator through 
which the current generated may be supplied to the 
switchboard in the power house and then to the line. 




/ ROTATING 
MAGNET POLES 



COPPER WIRE COILS 

ON CORES 



PULLEY 

MAGNET FRAME 



GENERATOR BASE 



Fig. 13 



If the generator illustrated in Fig. 13 operates at the 
speed of 1,800 revolutions per minute, we find from the 
rule that we should multiply the speed by the number of 
rotating pole pieces, which in this case is 4, making the 
calculation as follows : 

1,800 r.p.m. X 4 pole pieces = 7,200 alternations per 
minute. If we wish to reduce this figure to cycles divide 
7,200 by 2, which equals 3,600, and divide this by 60 sec- 
onds, equals 60 cycles. 

In making the diagrammatical sketch, Fig. 13, I have 
not attempted to make an actual representation of a gen- 
erator, but one which would plainly illustrate the differ- 
ent parts of the generator and their functions. You can 



MOTION PICTURE ELECTRICITY 45 

understand, of course, that there may be any number of 
pole-pieces and the design may be changed to suit the 
particular ideas of the designer. 

It has been stated that the current leaves the generator 
at the terminals and is transmitted through highly in- 
sulated cables to the switchboard. I wish to call your 
attention to the fact that alternating currents are usually 
generated at voltages varying from 1,000 up to 6,600 
volts, and you can understand that on account of the 
high voltage windings being stationary, therefore not 
subject to excessive vibration and also on account of hav- 
ing more room than on an ordinary rotating armature, 
it is possible to put on a greater quantity of insulation on 
the copper wire, which forms the magnet coils, and there 
is also plenty of room for insulation between the coils 
and the soft iron cores, permitting the high voltage above 
mentioned to be generated and sent to the switchboard 
without any danger either to the man who handles the 
machine or to the machine itself. 

I have illustrated the rotating magnet poles without 
complication and you may imagine that the poles are 
made from hardened steel magnetized so as to form per- 
manent magnets. In practice, however, it has been found 
to be more economical and preferable to put a copper coil 
on each one of the rotating magnet poles. The coils are 
connected in series and the two terminals are then con- 
nected to two "Collector Rings" — mounted on the shaft 
which rotates with it. Two copper gauze or carbon 
brushes rest one on each collector ring and direct current 
from a storage battery or from a small direct-current 
generator usually called the "exciter" is supplied to the 
brushes, allowing the direct current to flow from the 
collector rings, through the magnet coils on the rotating 
poles, which are thereby magnetized to any desired ex- 
tent under the control of the dynamo attendant who can 
increase or decrease, by means of a field rheostat, the 
voltage and current delivered by the "exciter." 

Fig. 14 illustrates the rotating magnet and collector 
rings, when the field magnets are excited by magnet coils 
through which direct current is flowing from a small 
direct-current generator. 



46 MOTION PICTURE ELECTRICITY 

Largealternating current generators are usually 
made with a number of rotating magnet poles, 
alternately of north and south pole magnetism. 

On account of the difficulty of securing a per- 
manent magnet of large size and also on account 
of the impossibility of regulating the strength of 
the magnetism from a permanent magnet ; the pole 



COLLECTOR BRUSHES 
(TAKE IN DIRECT CURRENT 
FROM D.C. EXICTER.j 




INSULATION 



Fig. 14 

pieces of an alternating-current generator are usu- 
ally magnetized by copper coils, through which di- 
rect current flows. 

The magnet poles of an alternating-current 
generator have to be supplied with direct current, 
which is usually furnished by a very small direct- 
current dynamo or generator, which is provided 
with its own field rheostat by means of which the 
attendant in the power house can increase or de- 
crease the voltage of the small generator, or 
"exciter," thereby increasing or decreasing the cur- 
rent flowing in the magnet coils on the magnet 
poles of the larger alternator, which in turn in- 
creases or decreases the voltage of the alternat- 
ing current delivered by the alternating-current 
generator. 



MOTION PICTURE ELECTRICITY 47 

CHAPTER III 

The Transformer for Alter- 
nating Current 



THE electric transformer is a device for producing 
a current of different quantity and potential than 
the supply current. In alternating-current light- 
ing or power systems, the transformer reduces the primary 
line voltage to a lower voltage suitable for the interior 
of buildings, in w T hich case it is called a "step-down" 
transformer. In some instances it is desirable, when 
transmitting electric energy, to generate the current at 
a low voltage, then for long distances where high voltage 
is required on the line wire, a transformer is introduced 
between the generator and the line wires for increasing 
the line voltage, in which case it is called a "step-up" 
transformer. 



CONSTANT POTENTIAL TRANSFORMER 

For general requirements, however, we need only con- 
sider the step-down transformer, which consists of sev- 
eral parts, which are diagram- 
matically illustrated in Figs. 15, 
16, 17, 18 and 19. 

There are several types 
of transformers, some in- 
tended to reduce from one 
voltage to another main- 



Fig. 15 





48 



MOTION PICTURE ELECTRICITY 



TO LINE 
1000 VOLTS 



taining the voltage delivered as nearly constant as 
possible, irrespective of the load. This type of 
transformer is called "constant potential." 

For other purposes transformers are required 
to reduce a given line voltage to a steady flow of 
amperes as may be required for a motion picture 
arc lamp or for operating arc lamps in series, as 
is usually done for street lighting, and this kind of 
transformer is said to be of the "constant current" 
type, because it maintains a steady ampere flow on 
the circuit which supplies the arc lamp, or in case 
of street lighting several arc lamps in series. 

For the present, we will only consider the step-down 
constant potential transformer, and referring to Fig. 15, 
the illustration gives a top view of the core, and Fig. 16 
gives an end view of the core. 

The core of an alternating cur- 
rent transformer is made up of 
sheets of annealed iron, or spe- 
cially prepared electrical steel. 
The sheets must be very thin; 
not more than 1-64 of an inch. 
The best transformers use sheets 
not over 1-100 of an inch thick. 
In constructing the core it is also 
necessary to provide a thin layer 
of insulation between every sheet 
of iron, and this is usually ac- 
complished by painting one side 
of the iron with some insulating 
compound. These sheets of iron 
are usually called "laminations," and a core made up from 
such sheets is called "laminated core." After the sheets 
have been stacked on top of each other to the desired 
thickness, which is determined by the size of the trans- 
former, they are insulated by fiber, press board and mica, 
so that the copper coils may be placed around the core 
legs without any danger of touching the iron. 

Fig. 17 illustrates the core, with the primary or high 
voltage winding in place. This winding is generally 




Fig. 17 



MOTION PICTURE ELECTRICITY 



40 



composed of a comparatively great number of turns of 
small insulated copper wire in the shape of coils sur- 
rounding the core legs. For argument sake, we might 
assume that this transformer has 1,000 turns of copper 
wire for the primary winding and that the line voltage 
is 1,000. 



& 



SECONDARY 
WINDINGS 



m 



TO LOAL 

100 VOLT 

Fig. 18 




Referring to Fig. 18, you see the secondary winding 
of this same transformer mounted on the core legs. This 
winding is composed of comparatively- few turns of larger 
insulated copper wire, and we may assume in this in- 
stance the two secondary coils are composed of ioo turns, 
which if connected to the load will deliver about ioo volts. 

Fig. 19 shows the complete transformer with laminated 
core, primary and secondary windings in place, making 
a complete transformer wound for 1,000-volt primary, 
and 100-volt secondary to be used as a "step-down" 
transformer. 

This same transformer illustrated in Fig. 19 can be 
used as a "step-up" transformer by connecting the 100- 
volt line to its secondary 100-volt windings, in which 
case they become primary and this transformer will de- 
liver on its secondary 1,000 volts, so that you can see that 



50 MOTION PICTURE ELECTRICITY 

the same transformer can be used for "step-up" or 
"step-down" work. 

The operation of the transformer is as follows: When 
the alternating current passes through the primary wind- 
ing it produces magnetism in the iron core, which is re- 
versed 60 times per second on a 60-cycle circuit. This 
magnetism, in turn, induces electric current in the sec- 
ondary windings and the voltage of this current will 
depend upon the number of turns of wire on the core. 
I have illustrated how the primary is wound with 1,000 
turns of wire for 1,000 volts, and the secondary with 100 
turns of wire for 100 volts. It is evident that this ratio 
which, in the above case, is 10 to 1, can be changed to 
any desired amount by putting more or less turns of wire 
on the primary and secondary coils. 

The transformer,, for alternating current, is a most 
efficient and useful device. In fact, it has made the alter- 
nating current of great value, because it permits generat- 
ing and transmitting high voltage currents of great 
power at low amperage over small wires to be reduced 
efficiently and with safety to low voltage currents and 
great power of higher amperage as is required for light- 
ing, power and heat. 

The transformer when reducing a high voltage 
is called "step-down" transformer ; when increasing 
the voltage, it is called "step-up" transformer. 

The transformer has three distinct parts: The 
laminated iron core, the primary winding and the 
secondary winding. 

The number of turns of the primary and sec- 
ondary windings determine the ratio of trans- 
formation. 

"Constant Potential" means steady or constant voltage 
and when used in connection with a transformer it sig- 
nifies that a change in voltage is required and that the 
delivered voltage must be maintained constant, or steady,- 
irrespective of the load. A constant potential transformer 
is the type required for electric power, incandescent lamps 
and constant potential arc lamps such as are usually em- 
ployed in factories, stores and theaters. 



MOTION PICTURE ELECTRICITY 



51 



It is not an easy matter to design and construct a trans- 
former which will regulate well, that is, hold the voltage 
steady, whether one lamp or the entire number of lamps 
connected are burning. If the transformer does not reg- 
ulate well, the voltage will be high when only a few lamps 
are burning and as more lamps or motors are switched 
on, the voltage will drop lower and lower. Modern trans- 
formers are constructed to give a practically constant 
voltage irrespective of the load, and the regulating qual- 
ity of a constant potential transformer depends mainly 
upon the amount of magnetic leakage. 

CONSTANT CURRENT TRANSFORMER 

If the magnetic leakage is great the transformer will 
not regulate well and the voltage will drop more and 
more as additional load is put on. 




Fig. 20 



Fig. 20 illustrates a transformer having considerable 
magnetic leakage because the primary and secondary coils 
are some distance apart and are mounted on separate legs 
of the iron core. When the line current passes through 
the primary coil it generates magnetism in the iron core 
and the current being alternating this magnetism is re- 
versed a given number of times per second, depending 
upon the frequency of the current. If the secondary coil 
is not connected to any load, the magnetism will pass 
through the iron as indicated by the arrows, first in one 
direction, then when the current reverses in the other 



52 



MOTION PICTURE ELECTRICITY 



direction performing no work, simply keeping the iron 
core "excited," and the secondary coil under tension. 

If we should now put load on the secondary coil as indi- 
cated by the arc lamp in Fig. 21, all of the magnetism will 
no longer pass through the core leg upon which the sec- 
ondary coil is mounted, but some of the magnetic lines 
of force will crowd over the air gap between the primary 




Fig. 21 

and secondary coils and these lines are therefore lost and 
are of no use in producing voltage in the secondary coil, 
allowing the voltage in the secondary to drop when the 
arc lamp is turned on. 

Therefore, you can understand that a transformer 
built as illustrated in Figs. 20 and 21 is a very poor con- 
stant potential transformer, in fact it would not do at all, 
unless a given number of lamps were always burning at 
the same time, because the voltage would fluctuate up 
and down as the number of lamps were decreased or 
increased. 

CONSTANT POTENTIAL WINDINGS 



In view of the foregoing it becomes necessary to place 
the primary and secondary coils of a constant potential 
transformer very close together and, as a matter of fact, 
modern transformers are built in sections with the pri- 
mary and secondary windings sandwiched between each 
other and in some instances the windings are one on top 



MOTION PICTURE ELECTRICITY 53 

of the other as illustrated in Figs. 22 and 23, in order to 
minimize the magnetic leakage. 




Fig. 22 




The core for a transformer may be of many different 
shapes. The type which has been previously illustrated 
is called the "core type," having two magnetic legs. 




Fig. 24 



Fig. 24 illustrates another type also much used, which 
is called the "shell type" transformer. In this design there 
are three legs, the middle one is usually of double the 
cross-section as compared with the two outside legs and 



54 



MOTION PICTURE ELECTRICITY 



the primary and secondary coils are mounted on the mid- 
dle leg as illustrated. 

Either the core type or shell type transformer gives 
satisfactory results and there are certain advantages 
claimed for both types. As a matter of fact as far as effi- 
ciency and regulation is concerned there is not much 
choice and either one may be used with safety and satis- 
factory results. The determining factor in making a se- 
lection of the two being simply a matter of choice with the 
designer. 



o a o 




V-V 

r= Sr ^\/ni -re ==*» 



Fig. 25 



VOLTS" 

Fig. 26 



The constant potential transformer must have 
the lowest possible amount of magnetic leakage in 
order to maintain the voltage constant irrespective 
of the amount of load on its secondary. 

In order to reduce the amount of magnetic leak- 
age, the primary and secondary coils of a Constant 
Potential transformer should be mounted very 
close together or one on top of the other on the 
same core leg. 
All modern constant potential transformers are usually 
made with two primary and two secondary coils, each 
coil having its terminals brought outside of the trans- 
former case, permitting the primary coils and secondary 



MOTION PICTURE ELECTRICITY 



55 



coils to be connected in series or parallel as may be re- 
quired for different voltages and for either 2-wire or 
3-wire system. 

Fig. 25 shows the four primary and four secondary 
terminals. Suppose each primary coil is wound for 1,000 
volts and each secondary coil for 100 volts, then if the 
connections are made as illustrated in Fig. 26, the trans- 
former may be operated on 1,000-volt line to deliver 100 
volts on the secondary, because the primary and secondary 
coils are now connected in parallel. 




200 VOLTS 

Fig. 27 




Fig. 28 



If the connections be made as illustrated in Fig. 27, 
then the coils being connected in series, the transformer 
would be adapted for operation on 2,000-volt line and 
to deliver 200 volts on the secondary. It is evident that 
by connecting the secondary as shown in Fig. 26 and the 
primary as shown in Fig. 27, you would have a trans- 
former adapted to operate on 2,000-volt primary to de- 
liver 100 volts on the secondary because the primary 
coils are in series and the secondary coils in parallel. 

Now we may go one step further and your attention 
is called to Fig. 28, in which you find the two secondary 
coils connected in series, but the middle wire brought out 
from the transformer, in which case the transformer 
would operate on 2,000-volt line and on the secondary 



56 MOTION PICTURE ELECTRICITY 

there would be available ioo volts between each of the 
outside wires and the "neutral" or middle wire and 200 
volts between the two outside wires. 

The foregoing illustrations represent correctly the 
following : 

Fig. 26, the 2-wire 100-volt system. 
Fig. 27, the 2-wire 200-volt system. 
Fig. 28, the 3-wire 100 and 200-volt system. 

Throughout the country there are many different sys- 
tems of distribution in use, and of these the three-wire 
system is perhaps the most complex and requires more 
care and judgment in its handling and installation. Re- 
ferring to Fig. 28 you have therewith illustrated a trans- 
former reducing from a 2,000-volt line to 3-wire 100 
and 200-volt secondary. This transformer is usually 
mounted on a pole outside of the building where the pri- 
mary wires are connected through two protecting fuses 
(usually mounted on the pole cross arm or made a part 
of the transformer itself) to the line wires. The three 
secondary terminals are then connected to the feed wires 
which go into the building, in fact in some instances the 
electric lighting company may place one transformer in 
the middle of a block where it is connected to the line 
wires, then the company will run three large wires along 
the block to which the three secondary terminals from the 
transformer are connected, thus feeding the three main 
wires running along the street with current at 100 to no 
volts between the "neutral" or middle, and each outside 
wire, and 200 to 220 volts between the two outside wires. 
Where one transformer is installed for the service of a 
whole block or for several adjoining buildings it is evi- 
dent that upon the regulation of this one transformer de- 
pends the constancy of the candle-power of all lamps 
connected to that particular transformer. It is the aim 
of all manufacturers of transformers to make the regu- 
lation as close as possible so that the voltage will be the 
same, irrespective of the number of lamps burning and 
the manufacturers have been very successful in accom- 
plishing these results, 



MOTION PICTURE ELECTRICITY 57 

It is a very difficult problem to build one transformer 
with two secondary windings connected to a three-wire 
system as illustrated in Fig. 28, which will maintain the 
same voltage on either side of the neutral wire irrespect- 
ive of the number of lamps burning and the nature of 
the load represented by incandescent lamps, arc lamps ; 
motors, etc. The 3-wire system as illustrated in Fig. 28 
under normal conditions is a balanced system, that is, if 
the voltage between the outside wires is 200 the voltage 
between the neutral and each outside will be 100. Sup- 
pose we connect a motion picture arc lamp between the 
neutral and one outside wire and there are no other lamps 
on the opposite side of the system or at least only a com- 
paratively small number of lamps, the side on which the 
motion picture lamp is connected may allow the voltage 
to drop to 90, but at the same time the voltage on the 
opposite side will go up to no. This, of course, makes a 
fluctuation in the candle-power of the lamps and besides 
it makes the motion picture lamp burn dimmer than it 
ought to. 

You realize that if this same transformer feeds a num- 
ber of lamps in neighboring shops and establishments a 
big kick will be registered with the electric lighting com- 
pany, due to the voltage fluctuation and consequent in- 
crease and decrease of candle-power of their lamps. This 
problem involves a careful system of balancing the load 
between the neutral and each outside wire of the 3-wire 
system and it also requires a carefully designed and 
constructed transformer. This is one reason why it is 
always well to consult the electric lighting company's 
expert or other competent authority when laying out the 
electric installation, especially when the 3-wire system 
is used. 

All modern transformers are made with two 
primary and two secondary coils, the terminals of 
all coils being so arranged that the primary and sec- 
ondary may be connected for either series or par- 
allel operation, which permits the same transformer 
to operate on two different voltages on both pri- 



58 MOTION PICTURE ELECTRICITY 

mary and secondary for either 2-wire or 3-wire 
system. 

When the 3-wire system of electric distribution 
is employed great care should be exercised in bal- 
ancing the load properly between the neutral and 
the outside wires so that the unbalancing of the 
voltage and consequent change in candle-power of 
the electric lamps will be reduced to a minimum. 



MOTION PICTURE ELECTRICITY 59 



CHAPTER IV 

Electrical Service 

IN the previous chapter careful discussion has been 
given to the fundamental rules governing the gen- 
erating and distributing of electricity. I have pur- 
posely avoided reference in particular or detail to the 
electric installation on the premises of the consumer of 
the electric current, limiting previous discussions to gen- 
eral information on how the electric light company gen- 
erates and distributes electricity to be used by the 
consumer. 

STREET SERVICE 

Fig. 29 is a plan view of a street showing part of a few 
regular building blocks. You will observe that the stores 
along the street are of different sizes, requiring a greater 
or less number of lamps, and the electric lighting com- 
pany has located its poles and wires on one side of the 
street. The section is intended to illustrate one or two 
business blocks where considerable electric current would 
be required. 

For the sake of simplicity I omit showing the high 
voltage wires, illustrating only the secondary wires from 
the transformer or the low tension wires of a regular 
2-wire and 3-wire direct-current system. In the illustra- 
tion the transformer mounted on top of one of the poles 
receives current from the high voltage system over two 
small wires, and this transformer feeds 2-wire or 3-wire 
main running along the street as illustrated. Suppose 
the electric light company gets a customer for store A 
and they require only eight or ten 16-candle-power incan- 
descent lamps, which would require approximately 5 am- 
peres at no volts. In this case it would not be necessary 
to bring all three wires into the building, so only two 



60 



MOTION PICTURE ELECTRICITY 




STREET 




MOTION PICTURE ELECTRICITY 61 

wires are brought in: namely, one of the outside and 
the "neutral" wire, as illustrated. This will serve the 
customer with no-volt current. 

Suppose a customer at E is running a factory where 
he wants a large electric motor installed, but he does not 
require any light, then the electric company would fur- 
nish him with current at 220 volts, in which case they 
would bring in the two outside wires of the system as 
illustrated. Suppose the theater in the center of the 
block wants current for incandescent lighting, ventilating, 
spot lights and motion pictures and stereopticon lights. 
In this case the electric company would bring in all of 
the wires, giving to the theater the regular 3-wire sys- 
tem, which delivers no volts on each side of the "neutral" 
and 220 volts between the outside wires. 

A new customer wants current at H for about ten 
incandescent lamps, then the electric company will run 
across the street with only two wires, giving no volts. 

If you closely study Fig. 29 you will find that this 
3-wire system is balanced because there are ten lamps 
in store A at one side of the 3-wire system which are 
balanced against ten lamps in store H on the opposite 
side of the system. The motor is on the two outside wires 
getting 220 volts in Factory E, which, of course, does not 
unbalance the system and the theater having all three 
wires brought in will give a balanced load to the system, 
providing the wiring and the arrangement of the lamps, 
motors, etc., is properly attended to by a competent elec- 
trical man. 

Suppose a motion picture theater starting at J re- 
quires electrical service for a motion picture lamp and a 
few incandescent lamps and that the building J has been 
wired for 2-wire system, the electric light company will 
be compelled to run only two wires to the building unless 
it is re-wired and the choice is one of the outside wires 
and the "neutral," in which case no volts is supplied, 
or the two outside wires which would deliver 220 volts. 
The motion picture man's machine, motors and fittings 
happen to be made for no volts there is only one choice 
and that is, the no-volt service. 

Suppose the system is alternating and the rheostat is 



62 MOTION PICTURE ELECTRICITY 

used, then for a good light two rheostats must be used 
in parallel or multiple. The motion picture lamp would 
draw around 60 to 70 amperes the instant the carbon 
points are put together and would normally require 
around 45 amperes. You can imagine how the pre- 
viously balanced 3-wire system referred to and illustrated 
in Fig. 29 would be disturbed every time the motion pic- 
ture at J is switched on and put in operation or when it 
is cut off. 

The result in practice would usually be that all cus- 
tomers connected on the same side of the 3-wire system 
as J would notice a considerable drop in the candle-power 
of their lamps, as would be the case in store H, and there 
would be a drop in candle-power of all lamps connected 
to the left-hand no-volt circuit brought into the theater 
on the opposite side of the street. On the other hand, 
the lamps in store A would burn brighter, as would also 
the lamps connected to the right-hand side of the electric 
service for the theater. 

This unbalancing has already been referred to in pre- 
vious chapters, but I want you to keep in mind the seri- 
ous inconvenience and disturbance to an electric system 
which has been subjected to unbalancing of the load. To 
operators of motion picture machines this point is of 
particular importance, because if the voltage drops below 
normal, the operator cannot produce results, and just be- 
cause you always had good current, that is no reason 
why tomorrow the condition may not be changed, pos- 
sibly due to one of your neighbors putting in a motor 
or additional lamps, and these may be connected to the 
same side of the system to which your motion picture 
lamp is connected, forcing the voltage below normal. 

I know of some instances where electric service has 
been run into a theater and everything appeared to be 
satisfactory for a long time. Suddenly the motion pic- 
ture lamp would not work properly, nor would the out : 
side arc lights, and the manager observed a considerable 
dip in the candle-power of his incandescent lamps every 
time the motion picture lamp was switched on. Upon in- 
vestigation it was found that the electric lighting com- 



MOTION PICTURE ELECTRICITY 63 

pany's linemen had connected another customer to the 
same wires and transformer which supplied the motion pic- 
ture theater, overloading the wires and the transformer, 
and the most natural thing in the world followed ; namely, 
a big drop in voltage, and consequently in the light, as 
less amperes can be put through the lamps with the lower 
voltage. Dissatisfaction follows, and the operator is un- 
justly blamed, in many instances, for troubles caused by 
interference in the electric system beyond his control. 
It really takes a voltmeter to tell whether the voltage is 
right or wrong and to what extent the voltage may drop, 
but an expert can also judge approximately the voltage 
drop by the dip in the candle-power of incandescent lamps 
connected to the system. 

With a given system of electric mains running in 
front of a number of buildings, whether 2-wire 
or 3-wire system, perfect results can be had if the 
voltage supplied to the mains is constant, the mains 
are of proper size, the transformer of proper size, 
and the load properly balanced between the 
"neutral" and each outside wire. 

With a system as that described above, great 
troubles may be experienced if the voltage varies, 
if the wires are too small, if the transformer is too 
small, or does not regulate well, and if additional 
load is added without consideration being given 
to the proper balancing of the load and the neces- 
sary increase in size of transformer, mains, service 
wires, electric meter, switches and fuses. 

I have referred to an installation for a motion picture 
theater in building J, of Fig. 29. By referring to it you 
will see that the load for this theater consists of the mo- 
tion picture lamp and a number of incandescent lamps, 
which had to be connected for no volts, and that in 
order to give this voltage, the electric light company had 
to use the neutral and one outside wire of the 3-wire 
system, and we also found that the system became un- 
balanced on account of this installation, which is, of 
course, undesirable, for reasons which have already been 



64 MOTION PICTURE ELECTRICITY 

explained. The inconvenience, from variations in the 
voltage, not only affects the operator in the motion pic- 
ture theater, as his light is likely to be poor, but it also 
affects other consumers supplied from the same system. 
In many instances the electric light companies find it con- 
venient to make such a connection, because it has to be 
made in a hurry, or they do not anticipate difficulties 
which might arise therefrom. A much better way would 
have been to supply the theater J with current from a 
separate transformer ; the primary of which could be 
connected to the high voltage primary line wires, and 
the no-volt secondary transformer wires could then be 
connected to the 2-wire service. This would overcome 
all trouble, and there would then be no voltage drop due 
to unbalanced load on account of the motion picture lamp 
in theater J. It is the aim of all electric lighting com- 
panies under modern management to avoid the unbalan- 
cing of a 3-wire system by putting in separate trans- 
formers and service for customers who have a load of 
such nature that it is likely to unbalance the system, but 
sometimes it becomes necessary for the manager or the 
operator of the motion picture theater to register a com- 
plaint about the drop in voltage when the motion picture 
lamp is switched on and the consequent rise in voltage 
when the lamp is switched off, and the sooner the electric 
light company is made aware of this voltage variation, 
and corrects it, the better for all concerned. 

INTERIOR SERVICE 

After proper mains have been brought into a building 
for the supply of electric current, a service switch with 
fuses of proper capacity must be installed as close to the 
entrance of the wires as convenient. The purpose of this 
switch is to disconnect entirely the electric current sup- 
ply from the building at night, so as to insure perfect 
safety and also give the proprietor absolute insurance 
that no lamp is burning which would cause the meter to 
register unexpectedly and unnecessarily. 

The electric lighting company will then install an elec- 



MOTION PICTURE ELECTRICITY 



65 



trie meter of proper size, and the wires from the meter 
may then be run to an electric distribution panel, which 
must contain the necessary fuses and switches for the 
protection of the various groups of lamps, fans, motion 



TO LINE 



LINE FUSES 



SWITCH 



A 



lA_& 



4 



Zo\ 



[oooej 



CIRCUIT FUSES^ 
CIRCUIT SWITCHES 



TO CIRCUIT 
TO CIRCUIT- 




METER 



Jo) 



BUS BARS 



PANEL OR 
DISTRIBUTING BOARD 



Fifr. 30 



picture machines, flaming arc lamps, spot lights, etc. The 
panel board referred to is usually located at a convenient 
point where the manager or other person in charge has 
full control of every circuit, permitting the turning on 



66 



MOTION PICTURE ELECTRICITY 



and off of the various circuits, and the fuses should be 
of proper capacity to protect the wires connected to the 
switches. 

The term "panel board" usually signifies a small switch 
board made of slate, upon which are mounted bus-bars, 
or copper strips, to which the mains are connected, in- 
cluding also the proper number and size of switches and 
fuses which are connected to the bus-bars. The various 
circuits are then connected to the switches. 



Two-Wire Service. — Fig. 30 is a diagram illustrat- 
ing a typical two-wire installation, including the fol- 
lowing: 

Line fuses. Line switch. 

Meter. Panel board for ten circuits. 

It is evident that in place of the panel illustrated, a 
cheaper form of distributing board can be constructed. 
For instance, in place of the board illustrated, there could 




TO CIRCUIT 



be used a number of double-pole, double-branch, com- 
bined cut-outs and switches mounted on the usual form 
of porcelain base as illustrated in Fig. 31. Wherever 



MOTION PICTURE ELECTRICITY 67 

panel boards or cut-outs are installed, they should be 
mounted in a suitable box, which should be made pref- 
erably of slate, or it should be lined with sheet iron and 
provided with a door lined with the same material, so 
as to make a practically fireproof cabinet, and the door 
should be provided with a lock, so that outsiders may 
not have opportunity to interfere with the fuses or 
switches. No panel box is complete without at least one 
extra fuse for each circuit ; to be on hand in case of an 
emergency. 

A panel board should always be examined at frequent 
intervals to make sure that all connections are tight, also 
to make sure that the fuse plugs, or any other form of 
fuse that are used, make good and perfect contact. The 
switches should occasionally be examined to see that the 
clips make good contact with the switch blade. A little 
vaseline or flaked graphite applied to the clips will prove 
advantageous and will increase the life of the switch, 
also insuring better operation. 

Attention to these small details will often prevent 
trouble, and there is one thing you should remember; 
that is, that a loose contact or an overloaded wire, fuse 
or other connection always costs money, because a loose 
contact or a small wire generates heat, and as this heat 
requires electric energy, it represents a useless expense, 
besides a loose contact will also lower the voltage to such 
an extent as to interfere with the proper operation of 
your installation. 

Electric service within a building must be amply 
protected by proper fuses and switches, and a suit- 
able distribution panel should be located at a con- 
venient point giving full control of all circuits 
within the building. 

Frequent examination should be made of all 
contacts, fuses, and switches to insure minimum 
loss and to improve the operation of the lamps and 
apparatus connected to the system. 

Three-Wire Service requires the usual protecting, 
metering, and distributing devices — the same as for 2-wire 
service, but in somewhat modified form, because of the 



68 



MOTION PICTURE ELECTRICITY 



fact that the 3-wire system has a third or "neutral" 
wire between the two outside wires, and instead of de- 
livering only one voltage it is possible to get two different 
voltages from a 3-wire system, which is often of advan- 
tage, and besides, it makes it possible to carry a heavier 
load with smaller wires, switches, fuses, etc. 



TO 
LINE 



T 



OUTSIDE WIRE 



OUTSIDE WIRE 



LINE SWITCH 



000 



[j [] [j 



1« U 



4 



ioi. 



OOOO 



CIRCUIT FUSES 
CIRCUIT SWITCHES 



TO CIRCUITS 110 V. 



220 V. 



3 WIRE FUSES- 



f ig. 32 



3 WIRE SWITCH- 






©rt+k'© 



rr. 



■oe-e/Q* 
oa-Bi(^«- / 

0- 



J" 



• Q*e-ao- 



8 WIRE CI RCUIT 6 . 11QV. 

FOB STAGE SP 110 V. 



4 




U" 






L.01 



ii~I~ii 
ii [i 



Fig. 32 is a diagram illustrating a typical 3-wire in- 
stallation, including the following: 

Three-line fuses. Three-pole line switch. 
Meter. Three-wire panel board. 



MOTION PICTURE ELECTRICITY 69 

The line fuses are connected to the 3-wire lines com- 
ing into the building. On the outside wires, there is usu- 
ally a pressure of 220 volts and between the "neutral" 
or center wire and either one of the outside wires the 
voltage would then be no. The wires leave the switch 
and go into the meter. From the meter three wires are 
run to the distributing panel board, which is clearly il- 
lustrated in Fig. 32. You will note that the three top 
circuits on each side of the bus-bars deliver no volts, 
because they are connected to the middle and one of 
the outside bus-bars alternately. The two lower switches, 
however, are connected to the outside bus-bars only, 
therefore the voltage available on the two lower circuits is 
220 as may be desired for large ventilating motors, mo- 
tion picture and stereopticon lamps or for spot lights 
operating on electric economizers. At the bottom of the 
panel board there is illustrated an additional set of three- 
pole fuses and a three-pole switch for a three-wire circuit 
as may be required for a separate section of a building, 
for instance ; in a theater the panel board may be in the 
front of the house where the electric company's service 
enters, and from this point all of the local circuits are con- 
trolled, but for the stage lighting a separate three-wire 
circuit may then be run to the stage to feed the panel board 
for the various stage circuits, auditorium lights, etc., 
which must necessarily be under the control of the stage 
electrician. This arrangement gives regular three-wire 
service for the stage practically independent of the other 
lighting circuits and gives also either no or 220-volt cur- 
rent for the stage as may be required for various types 
of appliances and lamps used for stage work. 

Fig. 33 illustrates a more simple form of three-wire 
distributing board made up of standard two-wire or three- 
wire cut-outs with switches and fuses mounted on the 
regular porcelain base. These may be mounted in a suit- 
able cabinet lined with slate or sheet iron, as already de- 
scribed, for the two-wire system giving perfect protec- 
tion and control of the various circuits. 

Note that in Fig. 33, for convenience sake, I have 
placed the three-wire branch circuit, switch and fuses at 



70 



MOTION PICTURE ELECTRICITY 



the top as may be required for a small stage circuit. 
Below is mounted three-wire to two-wire cut-outs de- 
livering no volts to each circuit and at the bottom there 
is a two-wire double branch cut-out connected to the two 
outside wires only, therefore giving 220 volts to each cir- 



110V. 



110V. 



'220 V. 




-BO 

o4a — BO 



-BO 



& — BO 



a — bo 



a — so 



a — bo 



110 V. 



110V. 
CIRCUIT 



110 V. 



a — ao 



a— -ao 



220 v. 



Fig. 33 



cuit. Any number of cut-outs of any desired type can be 
added or arranged in any suitable manner for giving no" 
or 220 for either two-wire or three-wire circuits. 

Whenever three-wire service is used, it becomes impor- 
tant to the operator and the electrician within the building 
to balance the load on either side of the system as per- 



MOTION PICTURE ELECTRICITY 71 

fectly as possible, the same as the electric light company 
must do it outside of the building. In fact, you should be 
even more particular about the balancing within the 
building because of the fact that your service is smaller 
and an unbalanced condition within the building is more 
likely to give trouble than unbalancing outside of the 
building. The balancing of the interior lighting is, of 
course, difficult to accomplish if a large unit like a motion 
picture arc lamp is connected to one side of the system to 
operate on no volts. Therefore it is always desirable to 
connect the motion picture lamp, stereopticon and spot 
lights to the outside 220-volt wires as illustrated in Fig. 33 
at the lowest cut-out. In that case it should be under- 
stood that when 220 volts is used and a rheostat is em- 
ployed for the control of such lamps, the load is twice as 
great as it would be with no volts, but the "balance" of 
the system is maintained perfectly, and by the use of an 
electric economizer the extra loss can be entirely done 
away with, thus maintaining the "balance" of the system. 

The three-wire service within a building re- 
quires careful balancing of the load, giving an 
equal' number of amperes on either side of the 
three-wire system. 

When motion picture, stereopticon, or spot 
lights, are operated on a three- wire system, it is 
better to connect such lamps on the outside or 220- 
volt wires. 

THE RECORDING WATT-HOUR METER 

When electricity was first offered for sale, the electric 
lighting companies generally made a contract with the 
consumer to supply him with current to operate a given 
number of lamps, motors or other devices. This flat rate 
allowed the consumer to use the lamps or devices as long 
as the current was maintained at his service. Such an 
arrangement or contract was unjust to all concerned, and 
after a few years the electric lighting companies found 
that it was absolutely necessary to secure some means 



72 MOTION PICTURE ELECTRICITY 

for measuring the exact amount of current required by 
each consumer and charge him therefor in accordance 
with the reading of the meter. 

A consumer, in the early days, may have had one hun- 
dred 16-candle-power lamps in his store divided on two 
or three floors. According to the old system he would 
be obliged to pay, we will say, for argument sake, $1.00 
for each connected 16-c.p. lamp per month. This would 
make his monthly bill $100, no matter how long or how 
many of the lamps installed were burning. 

The first step taken by the electric lighting companies 
was to secure means for determining just how many of 
the lamps installed were burning a given number of hours, 
and those figures were obtained by watching the installa- 
tion, in some instances secretly, to see just how many 
lamps were burning on the average. An ordinary indi- 
cating ampere meter was connected on the premises of 
the consumer and an expert was stationed there to take 
readings, many times a day and night, thus establishing 
an average figure for the consumption. Should the con- 
sumer add a few lamps or a fan motor to his installation 
or burn his lamps longer than usual or than contracted 
for, the electric lighting company would be the loser. On 
the other hand, should the consumer, as is the case during 
the light months of the year, burn his lamps a lesser 
number of hours, he would be the loser. 

These difficulties forced the electric lighting companies 
to demand from the electric manufacturers some form of 
electric meter, and as a result the recording ampere hour 
meter was offered for sale and installed in many instances 
by the electric companies. 

The recording ampere hour meter served its purpose 
twenty years or so ago, inasmuch as it registered on a 
number of dials the number of ampere' hours used by the 
consumer and who was charged in accordance therewith. 
As long as the voltage on the electric company's system - 
was maintained constant, and the load consisted of incan- 
descent lamps or other non-inductive load only, the re- 
cording ampere hour meter gave good satisfaction. 

Not many years after the introduction of the recording 



MOTION PICTURE ELECTRICITY 



75 



ampere hour meter, the manufacturers developed what 
is now known as the Recording Watt Hour Meter. 

The recording watt hour meter gives the instantaneous 
value of the watts expended in the circuit, and is, as its 
name indicates, a recording watt hour meter, and its read- 
ing gives the product of the watts and time, i. e., the watt 
hours. The construction is simple, the principle is, 
broadly, that of the Siemens Dynamo-Meter, which is 
composed of a stationary coil of copper wire in series 
with the load and surrounding this coil there is suspended 
another at right angles to the first coil and this outside 
coil is connected in shunt with the load, as illustrated in 
Fig. 34. In the recording watt hour meter, however, 



SWINGING COIL 

IN SHUNT 
WITH THE LOAD 



SUSPENSION CORD 



SCALE AND 
NDICATING POINTER 



STATIONARY COIL 
IN SERIES 
WITH LOAD 




Fig. 34 



the movable coil is not held to zero position, but revolves 
between two fixed coils. The movable coil is really a 
small drum-wound armature provided with a small com- 
mutator made of silver to prevent oxidization. The effect 
of using the commutator is to make the effective plane of 
the moving coil (armature) take a position at right angle 
to the plane of the fixed coils. 



74 



MOTION PICTURE ELECTRICITY 




MOTION PICTURE ELECTRICITY 75 

The connections of the recording watt hour meter are 
made on the same principle as those of the indicating watt 
meter illustrated in Fig. 34. The fixed coils are in series 
with the circuit and the movable coil and a small resist- 
ance in series with it are in parallel with the circuit as 
illustrated in Fig. 35. 

The amount of energy expended in the circuit is meas- 
ured by the rotation of the movable coil or armature, 
which rotates and drives a worm on the upper end of the 
armature shaft engaging with a set of gears which op- 
erate a dial similar to a gas meter dial so that the energy 
expended in a given time in a circuit may be read di- 
rectly from the dial in watt hours. 

The friction of the apparatus being exceedingly small 
the retarding force on the coil that opposes its tendency 
to rotate is imparted by a thin copper disk attached to the 
lower end of the shaft on which the armature is mounted. 
This disk is rotated between the poles of strong permanent 
magnets ; the lines of force from the magnets cutting the 
disk, set up electro motive forces between adjacent points 
on the disk; the disk being of copper, the resistance be- 
tween those points is very low, so that a considerable 
local current may flow in the copper disk. This current 
tends to retard the rotation of the copper disk, and this 
tendency increases directly as the speed. The force act- 
ing to rotate the armature increases directly as the watts, 
therefore, the number of revolutions of the moving sys- 
tem of the meter will be directly proportional to the watts 
expended in the circuit. This type of meter may be used 
for either alternating or direct currents, and gives very 
accurate results. 

The indicating watt meter is an instrument 
which, while applied to a circuit will indicate or 
show while it is under observation, the number of 
watts expended at a given instant in an electric 
circuit. 

The recording watt meter is an instrument which 
records the number of watt hours expended in an 
electric circuit by moving the hands on a set of dials 
the same as on a gas meter. 



76 MOTION PICTURE ELECTRICITY 

The recording watt hour meter is a very simple device 
consisting of an electric motor driving several hands on 
small dials. The speed of the motor depending upon the 
voltage of the circuit, and the current passing through 
the field coils and also depending upon what is known as 
the "Power Factor" of an alternating current circuit, 
when used with a. c, load. 

A rheostat or an incandescent lamp will operate at 
what is called "unity power factor," that is the voltage 
and current (the amperes) are in phase with each other. 
As a general rule, a rheostat is wound in the shape of a 
coil or spiral which makes it slightly "Inductive" when 
used on alternating current, but under ordinary conditions 

a rheostat or an electric heater and of course, in- 
candescent lamps may be considered to represent 
"non-inductive" load operating at "unity power 
factor." 

An electric motor, an arc lamp having magnet 
coils for its regulation, a motion picture arc lamp 
using an "Economizer," electro magnets and other 
devices, which contain one or more coils of wire 
having a number of turns, are put in the class called 
"inductive" load. 

All apparatus in the "non-inductive" load class operate 
at practically "unity power factor" and if you will refer 
to formula No. 4, on pages 20 to 22, you will find that in 
order to obtain the number of watts consumed in any 
given circuit, the amperes should be multiplied by the 
volts, and this method of calculating is correct for all 
"non-inductive" loads. 

Apparatus in the "inductive" load class do not 
operate at "unity power factor," but the current 
lags behind the voltage or electro motive force, 
therefore, if you multiply the voltage by the am- 
peres you will obtain a reading which represents 
what is called the "apparent watts." 

In order to measure the "actual watts" a watt 
meter is necessary because this instrument depends 



MOTION PICTURE ELECTRICITY 77 

in its operation not only upon the product of the 
voltage and the amperes, but also upon the phase 
relation between the voltage and the current. In all 
circuits carrying "inductive" load the current lags 
behind the voltage. 

Sometimes this lag may be 10 per cent., in which case 
the system is said to have a "power factor" of 90 per cent. 
An electric motor may operate on alternating current at 
an average "power factor" of 60 per cent. A motion pic- 
ture lamp with an "Economizer" may operate at a power 
factor of 80 per cent. A fan motor operating on alter- 
nating current may operate at a power factor of 50 per 
cent. The "power factor" becomes lower the more mag- 
netic effect there is in the circuit because the greater the 
number of ampere turns surrounding iron, the greater 
will be the magnetic kick as the current reverses, and con- 
sequently the current will lag more and more behind the 
voltage, due to the counter voltage set up by the magnetic 
kick or reaction in the coil. 

If the amperes and the volts multiplied by each 
other give a certain number of watts, this reading 
represents the "apparent watts" and in order to 
give the "actual watts" consumed the "apparent 
watts" must be multiplied by the "power factor." 

The indicating watt meter or the watt hour meter does 
all this work automatically, whereas, the volt meter, the 
ampere meter and the old recording ampere hour meter 
would only indicate the "apparent watts," which would 
be considerably higher than the "actual watts." 

Suppose we have a motion picture arc lamp, with an 
"economizer" operating on 100 volt a. c. circuit requiring 
20 amperes from the line; in that case multiply 100 volts 
by 20 amperes. This gives 2,000 "apparent" watts. 

We will assume that the "power factor" of the lamp 
and this economizer is 75 per cent. In order to find the 
actual watts multiply the "apparent" 2,000 watts by the 
"power factor" .75. This gives you just 1,500 watts or 
1.5 k.w., which represents the "actual" watts required 
per hour for such an arc lamp with the "economizer." 



78 MOTION PICTURE ELECTRICITY 

If this same motion picture arc lamp was operated with 
a choke coil or similar current saving device, on alternat- 
ing current the amperes "taken from the line would be 50, 
which multiplied by the 100 volts would equal 5,000 
"apparent" watts. The "power factor" of such a choke 
coil may be about 40 per cent., in which case, we should 
multiply 5,000 by 40, which would give us just 2,000 
"actual" watts or 2 k.w. 

Numerous other examples of this sort could be given, 
but I will go into more -detail concerning this matter later 
in the book. 

The watt hour meter as furnished and installed by the 
electric lighting company is a most accurate and reliable 
device. It is wrong for any consumer to believe, or even 
think, that any electric lighting company would willfully 
make its electric meters run fast or register when no load 
is on. I have personally had charge of one of the largest 
electric lighting plants in the United States where thou- 
sands of electric meters were in service and, I feel safe 
in making the statement that 90 per cent, of the errors 
in meters are in favor of the consumer because the elec- 
tric meter is a motor and it depends upon its frictionless 
bearings to keep it operating freely, therefore the least 
disturbance to which the meter may be subjected, such 
as the cracking of a jewel, the breaking of the shaft point 
working on the jewel, the accumulation of dust, the pres- 
ence of roaches or other insects within the meter, would 
stop it or make it run too slow. Do you believe that any 
public service corporation would willfully dare to instruct 
its meter testers to make a meter run faster than it ought 
to. Not a bit of it. The risk would be too great, because 
if one of the employees in the meter department should 
leave the corporation and could prove that the electric 
lighting company made a practice of setting its meters 
too fast, the company would soon be prosecuted. Acci- 
dents will happen, but the chances are that if the electric 
bill is too high and remains high after the electric lighting 
company has been instructed to that effect and have tested 
their meter, the large bill is due to your having more load 
connected to your system or the lamps, and other devices 



MOTION PICTURE ELECTRICITY 79 

are in use longer than expected. In view of the foregoing, 
I think you may feel quite safe in depending upon the rec- 
ord of the electric meter. 

The watt hour meter registers only the "actual 
watts" consumed. 

The "apparent watts" required by any load are 
determined by multiplying the amperes by the 
voltage. 

The "actual watts" are determined by multiply- 
ing the "apparent watts" by the "power factor." 

The "power factor" is obtained by dividing the 
"actual" watts by the "apparent" watts. 

Direct current devices always operate at "unity 
power factor." 

Alternating current devices, excepting incan- 
descent lamps, certain forms of rheostats, and 
heaters always operate at less than "unity power 
factor." 

HOW TO READ AN ELECTRIC METER 

In order to have a clear understanding of this part of 
your electric equipment, it is necessary that you should 
know how to read your electric meter. By understanding 
how to do this you are not only enabled to check the 
meter readings at the end of each week, or month, against 
the readings made by the electric light company's meter 
reader, but you can also, at your own convenience, read a 
meter for any given period during the day, or at the be- 
ginning and the end of a day, thereby determining for 
yourself just what it costs you to operate your electric 
system. 

Suppose you want to find out how much it costs you to 
operate your motion picture lamp on a rheostat. All you 
have to do is to start the motion picture lamp at the given 
time, keep it operating for ten minutes with no other 
lamps or loads on the meter, and, in the meantime, watch 
your electric meter record the current consumption. If 
your test is made for a period of ten minutes, multiply 
the reading by 6, which will give you the current consump- 



80 MOTION PICTURE ELECTRICITY 

tion for one hour ; and then multiply the product thus ob- 
tained by the rate for current per kilowatt hour. This 
will give you the cost of operating your motion picture 
lamp with rheostat for one hour. 

• If you wish to make a test of your motion picture lamp 
as controlled by the "economizer," proceed in the same 
manner and by that method you can, within ten minutes, 
determine the exact difference in current consumption 
with rheostat and economizer control. This test could be 
made in ten or fifteen minutes time, unless you wish to 
run a half hour or ^ 

so in order to get the 
more correct aver- 
age when no other 
lamps are burning. 
You can in that man- 
ner get an absolute 
record of the saving 
which otherwise 
could not be had un- 
less you had a sepa- 
rate meter for that 
part of your installa- 
tion which you want 
to test. 

By the same 
method you can test 
any part of your in- 
stallation as you can 
read the meter with 
only that portion of w 
your installation 
connected to it regarding which you want information. 

Through the courtesy of the General Electric Company, 
I have obtained the latest instructions for reading the 
electric kilowatt hour or watt hour meter, which I am 
sure will prove interesting and instructive. 

Before proceeding with the directions, I wish to call 
your attention to Figs. 36 and 37, illustrating the exterior 
and the interior of the Thomson watt hour meter. 




MOTION PICTURE ELECTRICITY 



SI 



DIRECTIONS 



First — Note carefully the unit in which the dials read. 
On all meters made by the General Electric Company, 
the figures above or below the dials indicate the value of 
one complete revolution of the pointer, therefore one di- 
vision indicates one-tenth of the amount marked above 
or below. 

Second — Note di- 
rection of rotation of 
dial pointers. Count- 
ing from the right the 
pointers of the first, 
third and fifth dials of 
the General Electric 
Company's meters ro- 
tate in the direction of 
the hands of a watch, 
whereas the pointers 
of the second and 
fourth dials move in 
the opposite direction. 

Third - — Read dials 
from right to left, set- 
ting down figures as 
read. 

Fourth — A 1 w a y s 
read the figure on 
each dial which has 
been last passed or is 
just covered by the pointer. 

Note carefully that each dial reading depends on the 
reading of the one next to it on the right. Unless the one 
before it has completed a revolution or passed the o, the 
pointer which is being read has not completed the division 
upon which it may appear to rest, and still indicates the 
figure last passed over. 

Fifth — See if the register is direct reading, i. e., has no 
multiplying constant. 

Some registers are not direct, but require that the dial 
reading be multiplied by a constant in order to obtain the 




Fig. 37 



82 



MOTION PICTURE ELECTRICITY 



true reading. If the register face bears the words, 
"multiply by j£," "multiply by 2," etc., the actual reading 
should be divided by two in the first case or doubled in 
the second, and similarly for other constants. 

Sixth — Subtract from the present reading the reading 
of last month, multiply the difference in kilowatt hours 
by the rate per kilowatt hour you are paying and you have 
the amount of your bill in dollars and cents. The ruled 
section illustrated in Fig. 38 will be found convenient for 
keeping a permanent record of each month's meter 
reading. 



Month 



January . . 
February 
March . . . 
April .... 

May 

June .... 

July 

August . . 
September 
October .. 
November 
December 



Present 
Heading 



Previous 
Reading 



Difference 



Fig. 38 

Earlier forms of General Electric Company's meters 
having five pointer dials reading in watt hours. Present 
types have four pointer dials reading in kilowatt hours. 

EXAMPLES OF DIFFICULT METER 
READINGS 



On page 83 w T ill be found examples of difficult meter 
readings, which may actually occur in practice. For in- 
stance, in Fig. 39, the dial on the extreme right reads 900. 
The second apparently indicates o ; but since the first has 
not completed its revolution, but indicates only 9, the sec- 
ond cannot have completed its division ; hence the second 



MOTION PICTURE ELECTRICITY 



83 



1000.000 100.000 10,000 




WATT HOURS 



Fig. 39 




Fig. 40 




KILOWATT HOURS 



Fig. 41 




KILOWATT HOURS 



Fig. 42 



84 MOTION PICTURE ELECTRICITY 

dial indicates 9 also. The same is true of the hand of the 
third dial; the second, being 9, has not quite completed 
its revolution, so the third has not completed its division ; 
therefore we again have 9. The same holds true of the 
hand of the fourth dial. The last hand (the extreme 
left) appears to rest on 1 ; but since the fourth is only 9, 
the last has not completed its division and therefore indi- 
cates o. Putting the figures down from right to left, 
the total reading is 999,900, though one might erroneously 
read 1,999,900, making a mistake of 1,000,000 units. 

By similar reckoning the value of other difficult indica- 
tions may be obtained as illustrated in Figs. 40, 41 and 42. 

It is of considerable value and of great satisfaction to 
any user of electricity to be able to read his own meter ; 
to determine the current consumption for any part of his 
installation and to calculate the cost, which can be readily 
done by following the foregoing instructions for reading 
the electric meter and multiplying the reading in kilowatt 
hours by the rate per k.w.h. 



MOTION PICTURE ELECTRICITY 85 



CHAPTER V 

Theater Wiring 

ARRANGEMENT OF ELECTRIC CIRCUITS 
AND LAMPS 

A CONSIDERABLE amount of money can be saved 
not only on the first installation cost, but also in 
the operation of the electric system for lighting a 
motion picture theater, by proper placing of the lamps and 
by selecting the proper style of fixtures. A clear under- 
standing of the subject also permits a proprietor to make 
the installation attractive to the eye, and another matter 
of no little importance is the possibility of arranging the 
circuits so that, in case of accident, certain lamps may be 
left on while other sections of the electric lighting system 
are disconnected, as may be necessary on account of fire 
or other similar accident. 

It is the object of this chapter to go into details concern- 
ing electric lighting arrangement, and I, therefore, call 
your attention to Fig. 43, which is a plan view of an or- 
dinary motion picture theater. 

The electric company's mains in this instance enter at 
the front and the main switch box No. 1 is located in 
the ticket booth, where there may also be located the nec- 
essary fuses and switches for the control of all circuits 
within and outside of the theater. 

Switch box No. 1 should contain two main switches ; 
one of which is outside of the meter to shut off the entire 
electric system. The second main switch shuts off all 
lamps but the exit and auditorium lamps. In addition to 
these switches there are of course separate switches which 
control each set of lamps, for instance: 

One switch for the flaming arc lamps. 

One switch for the sign. 

One switch for lobby lamps. 

One switch for exit lamps. 

One switch for auditorium ceiling lamps. 



86 



MOTION PICTURE ELECTRICITY 







© 



«o- 



-Qv> 











o)(> 



©>0- 



-Qv> 











v>0- 



V 

a 



gti 



OPERATING ROOM 




© BOOTH /? 



LOBBY 



Fig. 43 



© 



—\7 
#6 



MOTION PICTURE ELECTRICITY 87 

One switch for auditorium side lamps and the piano 
lamp. 

One switch for each motion picture machine, stereop- 
ticon or spot-light circuit. 

One switch for the lamps in the operating room, ticket 
booth and any other lamps for special purposes. 

There will also be one switch for supplying switch box 
No. 2 in the operating room, from which the ceiling lamps 
in the auditorium indicated by letter T can be switched 
on and off by the operator, but to be connected in shunt 
with another switch in the switch box No. i in the ticket 
booth. The purpose of this arrangement is to enable the 
manager or ticket seller to switch on the auditorium lamps, 
in case the operator should neglect to throw his switch 
when an accident or fire occurs in the operating room. 

This scheme of double control of the ceiling lamps in 
the auditorium is of great importance and ought to be ap- 
plied in all new theaters, and would be a good thing to 
apply in theaters already constructed. In case of fire in 
the operating room there is nothing which will more as- 
sist the proper dismissal of the audience than immediate 
illumination of the house. If the operator is the only 
man who can put on the house lights, as is the case in most 
theaters at this time, the house lights may never be 
switched on in case of fire in the operating room, because 
the operator will be too busy trying to put out the fire or 
to escape from the booth to save his own life, to think of 
anything else. When a switch is in the ticket booth or at 
some other convenient point, perhaps outside of the ticket 
booth, any person can immediately switch on the house 
lights, notwithstanding the fact that the operator's con- 
trolling switch in box No. 2 may be open, as it would be 
while he is running a picture. 

The arrangement, already referred to, provides for the 
connection of the exit light circuit ahead of the second 
main switch and fuse, which should be smaller than the 
first main switch and fuse. The object of this difference 
in the sizes of the fuses on the main switches is to make it 
impossible for the exit lights to go out, in case there 
should be a short circuit on the panel board or in the op- 
erating room, which might blow the fuses on main switch 
No. 2. 



ss 



MOTION PICTURE ELECTRICITY 



TO ELECTRIC CO.'S 
SERVICE — 



MAIN SWITCH 
NO. 1 



oooo 



FOR OPERATING ROOM, . 
OFFICE & CELLAR LAMPS - 



EMERGENCY SWITCH 
FOR AUOfTORIUM 
CEILING LAMPS 



FLAME ARCS. 




7 



~\ 



EXIT LAMP CIRCUIT 



SIDE LAMP CIRCUIT 



MAIN SWITCH 
NO. 2 



LOCATED IN 
\TICKET BOOTH 
V, OR IN 
/FRONT OF 
' THEATRE 



TO SIGN 

TO M.P. MACHINE 

TO SPOT OR STERIO LAMP 



LP— ~ 



AGE PANEL BOAR 



J 



TO EXHAUST FAN 
TO WALL FANS 
TO CEILING FANS 



SWJTCH BOX NO. 2 



OPERATING ROOM 



CIRCUIT FOR AUDITORIUM CEILING LAMPS 



Fig. 44 



MOTION PICTURE ELECTRICITY 89 

By selecting proper size fuses, for the different circuits, 
and by never using a large fuse inside of a smaller one, 
much trouble from "fuse blowing" can be avoided. There 
is nothing more annoying and in more instances so likely 
to cause uneasiness among the audience than to have the 
house fall into darkness unexpectedly. This should and 
can be avoided, by simply following the foregoing sug- 
gestions, which will be made more clear as we proceed. 

Give most careful consideration to the arrange- 
ment of the switches and fuses for the different 
sets of lamps and circuits in a motion picture the- 
ater in order to avoid total darkness of the house 
in case of accidental blowing of a fuse. 

Never put a large fuse inside of a smaller one 
for any circuit, unless, of course, there is some 
special reason for so doing; in general there is no 
such reason. 

Consult some competent authority on the electric 
installation for a theater, as, by so doing, much un- 
necessary expense can be obviated, and better re- 
sults obtained. 

Emergency and Exit Lighting. — Reference has been 
made to the necessity, or rather advisability, of providing 
an emergency switch for the control of the ceiling lamps 
T in the auditorium, as illustrated in Fig. 43. This emer- 
gency switch to be placed in switch box No. 1 in the ticket 
booth and connected ahead of main switch No. 2 on the 
panel board in the ticket booth, and then connected on 
the inside of the house light switch in the operating room, 
permitting the lighting of the house ceiling lamps, even 
though the switch for these lamps should be open in the 
operating room. 

Fig. 44 gives a diagrammatic view of the general ar- 
rangement of the electrical service, fuses, meter and 
switches for the various circuits and, when used in con- 
junction with Fig. 43 in the preceding talk, will be read- 
ily understood. 

In Fig. 44 the current from the street enters the main 
switch No. 1, which is equipped with 100 ampere fuses 
as an illustration. From this point the current passes 
through the meter. The wires then run from the meter 



90 MOTION PICTURE ELECTRICITY 

down through the small panel board, or a set of cut-outs, 
with switches for three or more circuits as follows : 

One circuit for exit lamps. 

One circuit for auditorium side lamps. 

One emergency circuit for auditorium ceiling lamps in 
shunt with the circuit for these same lamps controlled in 
the operating room. 

There may also be a circuit from this special panel 
board for office, cellar, operating room ceiling lamps, and 
other special lamps. 

The current then passes through main switch No. 2, 
which may be provided with 75 ampere fuses, as an 
illustration. 

From this switch the current passes to a panel or dis- 
tribution board, from which the various groups of incan- 
descent lamps, arc lamps, fan motors, exhaust fans, mo- 
tion picture machines, spot lights, etc., may be controlled. 

This arrangement makes the safest and most conven- 
ient means for controlling the electric circuits in a motion 
picture theater, and should always be applied to new in- 
stallations, and is also recommended for installation in 
existing theaters. By the expenditure of a few dollars, 
the necessary changes in an existing equipment can be 
made to accomplish these results. Every proprietor and 
manager will, no doubt, appreciate the advantage of being 
enabled to instantly light the auditorium ceiling lamps and 
to maintain the exit and side lamps burning at all times 
uninterruptedly, although the main fuse on the panel or 
distribution board may blow — due to an accidental short 
circuit. 

Operating Room Circuits.: — It is always well to pro- 
vide a separate circuit from the main panel board for each 
motion picture machine, spot light and stereopticon lamp 
and there should also be a separate circuit from the panel 
board to the switch box in the operating room, which is 
referred to as switch box No. 1, and switch box No. 2, in 
Fig. 43- 

Stage Circuits. — Where stage lamps are required, 
the various stage circuits including footlights, side lights, 
border lights, bunch lights, dressing-room lamps, flood 
and spot lights, should be terminated in a suitable panel 



MOTION PICTURE ELECTRICITY 91 

or distribution board located at a convenient point on the 
stage from which the stage electrician can control any 
group of lamps. The stage panel board may then be sup- 
plied with current by a circuit between it and the electric 
service in front of the house, but this circuit should be 
connected inside of main switch No. 2, so that in case of 
a short circuit on the stage panel board, the fuses on main 
switch No. 2 will blow, leaving the exit side and auditor- 
ium lamps still burning. 

Expert Advice. — It takes years of experience and in- 
timate knowledge of the peculiar lighting requirements 
of a theater to lay out the electrical equipment. It is sur- 
prising how few architects and electrical contractors un- 
derstand these requirements, and this accounts for the fact 
that, in many instances, installations are almost completed 
when changes have to be made often at considerable ex- 
pense to the owners. 

Much expense and trouble can be saved by employing, 
or consulting experienced, competent authority on these 
matters, and the saving not only means reduced cost of 
the first equipment, but also considerable saving on cost 
of operating. 

There are so many inferior electrical devices on the 
market, and new and improved devices are offered for 
sale almost every day, that the average man, even though 
in the electrical business, is not always up to date, and this 
is anothe reason why the best authority is none too good. 

Have specifications and plans prepared, no matter how 
small the job may be, and have specified therein the qual- 
ity and specific style of fixtures and goods wanted and let 
every bidder furnish a proposal on the same style and 
class of equipment, thereby putting each bidder on an 
equal basis, which will enable the owner to then choose 
with justice to himself and the bidder. The lowest bid is 
not always the cheapest, because workmanship and hon- 
esty in carrying out the work contracted for are worth 
more than the difference in some bids. 

The front of a motion picture theater is gen- 
erally the safest and best place to locate the electric 
service switches and panel or distribution board. 

The service switches and distribution board if 



92 MOTION PICTURE ELECTRICITY 

placed in the ticket booth should be accessible from 
the outside, by means of a door or window enabling 
the manipulation of the switches from the outside 
in case of fire. 

All switches should be properly labeled. 

There should be two main switches ; the first one 
having a 25 per cent, to 50 per cent, heavier fuse 
than the second switch, and between these should 
be placed the cut-outs and switches which control 
the circuits for exit and auditorium lights. 

LIGHTING FIXTURES AND LAMPS 

In making selection of electric lamps and fixtures for 
the illumination of a motion picture theater, one is con- 
fronted with a dozen or more types of electric lamps, and 
hundreds of different designs and styles of fixtures, so 
that the selection of these is rather difficult, unless some 
general rule is followed. 

You must approach this subject with your mind made 
up to secure an efficient, practical and artistic equipment. 
All of these good qualities cannot always be had at the 
lowest price, but suitable equipment can be had at a suffi- 
ciently low price to warrant anyone, when building a mo- 
tion picture theater, to consider only a proper equipment, 
and it is the object of this section division to give you a 
few pointers on what may be considered good methods. 

OUTSIDE ILLUMINATION 

The Flaming Arc. — For the outside of a motion pic- 
ture theater I do not believe there is any illuminating me- 
dium which is as economical and, at the same time, as 
effective in drawing patrons to the front of the theater, 
as the flaming arc lamp. The flaming arc lamp is a com- 
paratively recent invention, and two lamps are usually 
operated in series on either direct or alternating current. 
A good lamp of this type will produce over 3,000 candle- 
power and carbons, for it can be had giving either golden 
yellow, or a brilliant white light. The flaming arc lamp 
is comparatively simple and, if properly taken care of and 
trimmed, will last a long time. Two flaming arc lamps K 

x 



MOTION PICTURE ELECTRICITY 93 

cost anywhere from $100 to $125 installed, and two lamps 
together consume approximately one kilowatt of current 
per hour, which, at the ten-cent rate, makes the operation 
of the two lamps about ten cents per hour, with an addi- 
tional expense of about one and one-quarter cents per 
hour for each lamp for carbons. 

The Electric Sign is another attractive illuminating 
medium for the front. It can be made as plain or as elab- 
orate as desired, costing anywhere from $50 to $1,000 or 
more. A cheap inartistic sign is, in my opinion, not a 
paying investment. An attractive electric sign costs a 
great deal of money to put in and also costs a considerable 
amount to operate. The average price for a good sign 
for a motion picture theater is about $200 complete, in- 
stalled, and the cost of operating such sign is about 20 
to 40 cents per hour at the ten-cent rate, depending, of 
course, upon the number of lamps required. 

Decorative Front Lighting. — Another attractive 
form of exterior illumination for a theater, is the outlin- 
ing of the front with a number of 2 or 4 candle-power in- 
candescent lamps. These lamps can be arranged in many 
attractive ways and, by selecting different and harmon- 
izing colors, beautiful effects can be obtained. But this 
form of lighting is expensive to install and quite ex- 
pensive to operate. As a guide, I may state that at the ten- 
cent rate for current, it costs about two-tenths of a cent 
per hour for each 4 candle-power lamp and twelve one- 
hundredths of a cent for each 2 candle-power regular car- 
bon filament lamp. 

Advertising Value. — The value of an electric sign, or 
decorative lighting, in front of a theater, can be increased 
considerably by the use of electric flashers to switch 
groups of lamps on and off, making an animated and 
brilliant display. In the larger cities, these more or less 
fancy illuminations pay because of the transient trade; 
which in that way can be attracted, but I do not believe 
that any great expense for outside lighting display is war- 
ranted in a smaller town or in settled districts where there 
is no competition. 

Remember, that the exterior illumination of a theater 
takes the place of the newspaper advertisements of a 



94 MOTION PICTURE ELECTRICITY 

regular business house and is intended to attract the at- 
tention of the public. A theatrical manager can make 
no worse mistake than to spend a lot of money on the 
outside of his theater at a sacrifice of his program. If he 
does, he is in the same position as the merchant who ad- 
vertises extensively and then does not have the facilities 
for selling or delivering the goods properly and promptly. 
The answer is the same in both cases, the public may bite 
once, but not the second time. It is far better to use a 
moderate amount of display lighting outside and making 
the exhibition on the screen the best that can be produced, 
because that is what counts. 

Lobby Illumination. — The lobby of the ordinary 
motion picture theater is, as a general rule, a compara- 
tively small space to illuminate, especially in the larger 
cities where ground is valuable. It is not necessary to 
make a very extensive display of electric lamps in a lobby, 
because it can be seen only from across the street, and 
therefore, sufficient illumination of entrances and exits, 
and to enable the public to read your signs, is all that is 
necessary. It is, of course, a matter of taste with each 
individual owner as to how far he should go in the dec- 
orative illumination of the lobby of his theater. I feel, 
however, safe in recommending two or more simple, but 
artistic and efficient fixtures; each one equipped with a 
large Tungsten lamp for emergency use when the flaming 
arcs are out for any reason. These may be of any de- 
sired size from 60 to 250 watts. 

Figs. 45 and 46 give a good idea of fixtures for lobby 
illumination. Fig. 45 is a simple, one-light ceiling pen- 
dant fixture, equipped with a keyless socket, glass shade 
and Tungsten lamp of proper size. This fixture is plain, 
durable, inexpensive and efficient. 

Where a more ornamental fixture is desired, something 
along the style of Fig. 46 may be used or any other fix- 
ture possibly in the way of a lantern or something similar. 
The fixture in Fig. 46 is practically the same as that 
shown in Fig. 45, but to it, is added a shade which may 
be on the Japanese style made of bamboo frame with col- 
ored paper or silk body having a glass bead fringe at the 
bottom, or where a more permanent and expensive fix- 
ture is desired, this general design can be had with the 



MOTION PICTURE ELECTRICITY 



95 



dome made of leaded glass. When the ceiling of a lobby 
is low, the lamps may be put in a receptacle close to the 
ceiling, doing away with the stem of the fixture. A very 
pretty effect can also be had by a regular ceiling fixture 
having an 8 to 12-inch frosted, colored, or cut glass bowl 
under the lamp fitting in a ring screwed against the ceil- 
ing. Rich effect can also be had by installing a handsome 
three-armed bracket on each side wall of the lobby and 
possibly one on each side of the ticket booth window. 

I have noticed many installations where incandescent 
lamps have been applied for decorative illumination of 




Fig, 45 




46 



the lobby and where this form of lighting has been a 
complete failure, and only in special instances do I recom- 
mend the placing of incandescent lamps in rows and cir- 
cles, for the decorative illumination of a lobby, but only 
when you have decorations worth while showing. 

Flaming arc lamps are, as a general rule, the 
cheapest and most efficient illuminating medium 
for the exterior of motion picture theaters. 

Electric signs can be used to advantage in some 
cases, but are generally too expensive and are, in 
most instances, unnecessary. 

Incandescent decorative lamps in front of a the- 
ater are attractive, but too expensive to install and 
operate and are not generally necessary. 



96 MOTION PICTURE ELECTRICITY 

Simple and artistic electric fixtures, preferably 
few in number, make good form of illumination 
for the lobby of a motion picture theater. 

INTERIOR FIXTURES 

The motion picture theater is essentially a dark place, 
which outside of a limited amount of illumination requires 
very seldom any great amount of light. It is, of course, 
understood that where vaudeville (which should have no 
place in a first-class motion picture theater) is used, it 
may be necessary to provide a considerable amount of 
general illumination, but under normal conditions a mo- 
tion picture theater confined to the exhibition of pictures, 
and illustrated songs, needs only a fair amount of general 
illumination in order to enable the proper discharge of 
the audience at the end of the performance. 

It is well to provide sufficient subdued illumination dur- 
ing the entire time the theater is open to enable anyone to 
find a seat while the picture is on the screen. When pic- 
tures were first put in theaters, it was thought necessary 
to have the house absolutely dark, excepting for a few exit 
lights, but the tendency of to-day is to have the house 
partly lighted all the time. This necessity for illumina- 
tion during the time the picture is shown, calls for proper, 
and in some instances skillful application of lamps, in 
order not to interfere with the picture, and at the same 
time give a fair amount of general illumination. 

Many proprietors have made the mistake of equipping 
their theaters with rows of incandescent lamps in the ceil- 
ing of the auditorium, and in some instances, I have ob- 
served the entire frame for the screen outlined with incan- 
descent lamps. These installations are not only expensive 
to install and to operate, but they are in most instances 
unsightly, unless very carefully arranged on specially 
constructed and ornamental ceilings. There can be noth- 
ing more offensive to the eye than to have the picture 
disappear from the screen and then have the screen illu- 
minated by incandescent lamps placed on the frame. This 
arrangement gives a brilliant display of light which is dis- 
agreeable and besides it causes the pupil of the eye to con- 



MOTION PICTURE ELECTRICITY 97 

tract, so that when the picture is put on again, it takes the 
eye quite some time to adjust itself to the sudden dark- 
ness and to the much milder light on the screen when the 
picture is put on. It is only natural that this method takes 
away from the effect of the picture at least for some time, 
after it is put on and should, therefore, be avoided as 
much as possible. 

The general illumination of the auditorium can, of 
course, be had in many different ways. Fixtures and 
lamps costing from a few dollars each to $100 each, may 
be put in at the option of the owner. But why should a 
great amount of money be. expended for the purpose of 
ceiling lighting when it is not required in a first-class 
motion picture theater at any time excepting during the 
short space of time the theater is being filled or at the end 
of the performance in the evening when the audience 
passes out? Great expense for the general illumination 
of a motion picture theater is in most cases not warranted. 
Let us look back to Fig. 43 on page 86, where you will 
find a number of electric outlets designated as follows : 

E are exit lamps, which in the cheaper theater may be 
ordinary incandescent lamps of 2 or 4 candle-power, col- 
ored red. In the more expensive theaters special signs 
may be provided over each exit, consisting of a metal box 
having the words "Exit" in letters four to eight inches 
high, with the outline of a hand pointing to the location 
of the exit, if necessary, as illustrated in Figs. 49 and 50. 

S are brackets which may be of any suitable design, 
for instance, like Fig. 47, which is about the simplest and 
cheapest type available for the purpose. More elaborate 
fixtures can be put in if necessary. Fig. 47 with a 25-watt 
Tungsten lamp will answer for all general purposes, and 
it is well to have the side lights of the combination gas 
and electric type so that in case of failure of the electric 
current, the gas burners can be lighted in a few moments. 

T are the ceiling outlets. Fixtures for these can be of 
a design similar to Figs. 45 and 46, consisting of an or- 
dinary pendant or ceiling fixture in the socket of which 
may be supported a large Tungsten lamp varying in size 
from 60 to 250 watts, as may be required. These fixtures 
can be equipped with the ordinary glass shade or a more 



98 



MOTION PICTURE ELECTRICITY 




Fig. 47 



I I 



a 



Fig. 48 



EXIT3^ ^(EXIT 



^ 



Fig. 51 



RIGHT LEFT 

Fig. 49 F 'S- 5 



CEILIMG 

\W\JTiI 




Fig. 52 




Fig. 54 



MOTION PICTURE ELECTRICITY 99 

ornamental dome shade can be put on, making the installa- 
tion simple, but at the same time substantial, efficient and 
attractive. 

For the piano a suitable fixture with 4 candle-power 
lamp is sufficient and a design something similar to Fig. 
48 standing on top of the upright piano, having its shade 
adjusted to throw the light on the sheet music, is very 
desirable. No make-shift should be allowed for a piano 
lamp, because it is important that as little light as possible 
be reflected or directly visible to the audience. 

The subdued illumination during the time the picture is 
on the screen can be secured from special brackets or fix- 
tures provided with very deep cone shades or other suit- 
able reflectors, which will allow the light to be thrown in 
any direction desired, but under no circumstances must 
this light be directed against the screen, nor against the 
audience. 

Fig. 51 may be a simple pendant fixture with a socket 
having a 25-watt Tungsten lamp provided with a very 
deep cone shade. This fixture will throw the light down- 
ward and the depth of the cone shade as well as its nar- 
row angle will practically conceal the lamp. 

Fig. 52 is similar to Fig. 51, but in this case the cone 
shade is reversed, and of wider angle, allowing the light 
to be reflected against the ceiling, which gives a very 
desirable general illumination while the picture is being 
exhibited. 

Fig. 53 is a side bracket, which may be installed in place 
of bracket S on Fig. 43, or these brackets may be in- 
stalled in addition to the regular side bracket fixtures used 
for general illumination. 

Fig- 54 gives a side view of bracket Fig. 53 and illus- 
trates how the light may be reflected against the wall, 
giving a soft and diffused illumination. 

The 25-watt Tungsten lamps used in Figs. 51, 52, 53 
and 54 may be colored to suit the ideas of the manager. 
I have found that lamps colored amber give the best 
results. 

Indirect Lighting. — Where the design of the ceiling 
permits, and the decoration warrants the illumination of 
the ceiling, the auditorium as well as the lobby may be 



100 



MOTION PICTURE ELECTRICITY 




Fig S4-A 



MOTION PICTURE ELECTRICITY 



101 



illuminated by indirect lighting fixtures. These fixtures 
can be had in many varied designs. The plain ones, con- 
sisting of a reflecting bowl fastened to a stem with can- 
opy from the ceiling or hanging 
on three chains or hooks, selling at 
anywhere from $7 to $10 each. 
The more ornamental indirect 
lighting fixtures, as illustrated in 
Fig. 54A, sell at anywhere from 
$15 to $100 each, depending upon 
the size and the design. The use 
of these fixtures eliminates entire- 
ly the downward rays of light. 
The light is reflected from the in- 
side of the bowl against the ceil- 
ing, by which means it is evenly 
diffused throughout the auditori- 
um. It is evident that this form 
of fixture shows to best advantage 
where the ceiling is well decorated 
and finished to make an ornamen- 
tal appearance. 

The same form of fixture may 
be equipped with a semi-transpar- 
ent or opal bowl, in which case the 
illumination becomes semi - indi- 
rect. This means that part of the 
light will be reflected from the in- 
side of the opal bowl against the 
ceiling, and part of the light will 
be diffused through the opal bowl, 
which will radiate a soft light, the 
intensity of which will depend 
upon the thickness and density of 
the glass and the size of the lamp 
used. The semi-indirect fixture is 
illustrated in Fig. 54 B, and beau- 
tiful results can be obtained with 
these fixtures by using tinted or 

colored lamps. The lamp within the bowl may be 
dipped or otherwise colored, an amber color, for in- 
stance. This will soften the light and give a very pleas- 




Fig. 54-B 



102 MOTION PICTURE ELECTRICITY 

ing effect in the auditorium, or in the lobby, for which this 
style of fixture is equally well suited. The decoration of 
the ceiling is not so important with the semi-indirect 
fixtures, because any apparent lack of, or defect in, the 
decoration will not be so noticeable as when the straight 
indirect lighting fixture is used. In the more modern 
theaters the indirect as well as the semi-indirect style of 
lighting for the auditorium has been generally adopted. 
The principal advantage of this system lies in the fact 
that the auditorium may be kept well illuminated without 
detracting from the clearness and brilliancy of the motion 
picture. There is also the advantage that seats may be- 
readily found by incoming patrons without the help of an 
usher. 

Unless the ceiling of a theater is of ornamental 
and artistic design, it is not good practice to install 
groups or rows of incandescant lamps for general 
illumination of a theater. Simple pendant fixtures 
with large Tungsten lamps with a suitable reflector 
or shade are preferable and proper. 

Do not put incandescent lamps on the frame of 
the motion picture screen. 

Use a piano lamp of proper design to confine the 
rays of the light to the sheet music. 

If possible, use combination gas and electric fix- 
tures for the side lights. 

Install a limited number of lamps for general 
illumination while the picture is being exhibited 
but take care that the light rays from the lamps 
are confined to given directions, and the illumina- 
tion from these must never strike the screen nor be 
within direct vision of the audience. 



MOTION PICTURE ELECTRICITY 103 

CHAPTER VI 

Direct Current Projection 

ELECTRICITY is a force of power usually trans- 
mitted over a circuit of copper wire, and as long 
as the two wires are insulated from each other 
this force or power is confined to the wires and is avail- 
able for the production of heat, light or power at any 
point of the circuit. 

It has been stated previously that electricity may be 
produced by chemical action, as in the galvanic battery, 
and also by mechanical force exerted upon the rotating 
element or part of an electric generator also, called a 
"Dynamo." 

In order that you may understand in the most elemen- 
tary way what takes place in an electric circuit, incan- 
descent lamp or arc lamp, when the electric current passes 
through it, I have thought of, and herewith present, a few 
simple comparisons, which I hope will enable you, in 
your own way, to grasp and understand the reason why 
a wire gets hot; why the incandescent lamp glows and 
the arc gives a brilliant display of light rays. 

The first example, or comparison, will be a cannon ball 
moving at high velocity through still open air, under 
which condition its movement would be retarded to the 
lowest extent (unless, of course, we could imagine the 
ball flying through a vacuum without the effect of the 
influence of gravity or other similar force), the same as 
the electric current is retarded to the least extent when 
moving through a conductor in which the resistance to 
the current is very small. 

Now let us force the cannon ball through an opening 
like a tube for instance. Under this condition the ball 
will be retarded to an extent depending upon the diam- 
eter and the length of the tube. If the tube is very long 
the resistance will be greater. If the tube is small in 



104 



MOTION PICTURE ELECTRICITY 




W 



I'l I 



'I 





/ /; w 



1 1 



r I 



M \ 




IT) 



Jill llll V 



MOTION PICTURE ELECTRICITY 105 

diameter relative to the ball, the retarding effect will be 
still greater, due to the friction between the inside surface 
of the tube and the ball. If the tube which retards the 
movement of the ball is massive, the friction will simply 
stop the ball, or at least diminish its speed greatly, and 
there will be no other noticeable effect, because the mass 
of which the tube is composed will have absorbed and 
dissipated the heat generated by the friction. 

If, however, the tube is made of comparatively thin 
material, then the friction created might be great enough 
to make the tube heat to such an extent that it will glow 
and give out rays of light. If the tube were made still 
smaller in diameter the friction might be great enough to 
melt or ignite the material of which the tube is made. If 
the end of the tube is sealed up, the tube may glow, due 
to the friction throughout its length, but at the end of 
the tube where the ball strikes the stop, there will be an 
explosion, which manifests itself in stopping the ball or 
destroying the end of the tube — tearing or melting it 
away, as the case may be. The greater the speed of the 
ball, and the larger and heavier it may be, the greater will 
be the effect it can produce, and, as above stated, this 
effect may show itself in the shape of heat, light or con- 
cussion with consequent destruction, until the ball finally 
stops. 

Let us imagine a rapid-firing gun forcing one ball after 
another through a tube some distance away from the gun ; 
in this case we could make the tube heat to such an extent, 
due to the friction, that it would glow and be a source of 
heat and light, proving to you that almost any moving 
body or force creates heat if its movement is retarded or 
minimized. 

For a clearer explanation I submit Figs. 55, 56, 57 
and 58. 

Fig. 55 illustrates a cannon ball in motion in a given 
direction through space, just the same as an electric cur- 
rent would travel over a circuit of low resistance. 

Fig. 56 illustrates the cannon ball entering a tube where 
its motion is retarded, which creates friction, and the re- 
sult is heat and possibly a glow and consequent genera- 



106 MOTION PICTURE ELECTRICITY 

tion of light in the tube. This is the same as when an 
electric current is forced through a circuit which is too 
small for the quantity of amperes, making the wire heat 
and, under some conditions, causing the conductor to 
glow, giving off heat as in electric heater, or rays of light 
as in the incandescent lamp, also called the "glow lamp." 

Fig. 57 illustrates the cannon ball entering a tube which 
is contracted at the point A, causing a part of the energy 
stored in the moving ball to be dissipated at the point A, 
due to friction giving off heat and possible melting or de- 
stroying the tube at the point A. 

At this moment I want you to imagine that we could 
replace the destroyed material at A as rapidly as the suc- 
cessive cannon balls passing through the tube expend 
their force at this point through friction, giving off heat 
and possibly light. The effect of this arrangement, if it 
were practical, would be to produce a constant source of 
heat, and possibly light, at point A, giving us a compari- 
son with the electric arc as follows : The tube in Fig. 57 
joined together by the obstruction A takes the place of 
the two carbons in an arc lamp. The obstruction A repre- 
sents the electric arc, and the successive cannon balls rep- 
resent the electric current passing from one carbon over 
the air gap, producing the arc, then over the second car- 
bon back to the line, thus completing the continuous cir- 
cuit and performance. 

Fig. 58 illustrates the moving cannon ball encountering 
a dead stop at B, at which point the ball will either stop 
or expend the power within it with great force destroying 
the end of the tube, and this illustration gives an excel- 
lent comparison of the effect of an electric current when 
the carbon separation is so great that the arc cannot be 
maintained, causing the current to stop flowing, or, in 
representing a short circuit when the two carbon points 
are put together without sufficient resistance or other 
protecting element in the circuit, in which case there 
would be a great deal of power expended at the carbon 
points, resulting in an explosion and consequent destruc- 
tion of the apparatus. 

It is extremely difficult to make this matter much 
clearer to you because the electric current is a continuous 



MOTION PICTURE ELECTRICITY 107 

force, whereas in the instance of the cannon ball the force 
is necessarily intermittent, and besides, it is possible to 
stop the flow of current by simply separating the two 
wires, whereas with any other forces or power the stop- 
ping of the movement cannot be effected without trouble 
and great loss due to the momentum or inertia of the 
moving body which has to be brought to a standstill. 
Electricity has no momentum or inertia: it stops the in- 
stant the contact is broken and starts instantly, exerting 
full power the moment the contact is made. 

The Voltaic Arc. — When an electric current passes 
through a conductor, there is a loss caused by the re- 
sistance of the conductor to the passage of the electric 
current, which manifests itself in heat. 

If at a given point the conductor be made small in 
cross-section, or be made from a material of relatively 
high resistance, a considerable amount of heat will be 
generated at such point; in fact, the wire can be made 
to glow and give light. 

When the terminals of an electric circuit are separated, 
there will be a gradual increase of resistance to the pas- 
sage of current at the point of separation, and with small 
currents of comparatively low voltage, when the terminals 
are separated further, there will appear a small spark. 
This spark, which was in the early days produced by the 
current from galvanic batteries, was called by some of 
the early experimenters the "Galvanic Spark." 

The voltaic arc was probably first observed, and ex- 
perimented with to a considerable extent, by Davy, in 
1802. Davy attached to the poles of a large battery, com- 
posed of a great many cells, wires connected with carbon 
rods, which he first allowed to touch each other and then, 
when slowly separating the carbon points, he obtained a 
brilliant light or flame, nowadays referred to as the "Elec- 
tric Arc." 

For a general explanation of the voltaic arc, I quote 
T. O'Conor Sloane, A. M., E. M., Ph. D., as follows : 

The voltaic arc is the arc between two carbon 



108 MOTION PICTURE ELECTRICITY 

electrodes slightly separated, which is produced by 
a current of sufficient strength and involving suf- 
ficient potential difference. The penails of carbon 
are made terminals in a circuit. They are first 
placed in contact, and after the current is estab- 
lished they are separated a little. The current now 
seems to jump across the interval in what some- 
times appears an arc of light. At the same time 
the carbon ends become incandescent. As regards 
the distance of separation with a strong current 
and high electro motive force, the arc may be 
several inches long. 

The voltaic arc is the source of the most intense 
heat and brightest light producible by man. The 
light is due principally to the incandescence of the 
ends of the carbon pencils. These are differently 
affected. The positive carbon wears away and be- 
comes roughly cupped or hollowed ; the negative 
also wears away, but in some cases seems to have 
additions made to it by carbon from the "positive" 
pole. All this is best seen when the rods are slen- 
der, compared to the length of the arc. 

It is undoubtedly the transferred carbon dust 
which has much to do with this formation. The 
conductivity of the intervening air is due partly, 
perhaps, to this, but undoubtedly in great measure 
to the intense heating to which it is subject. But 
the coefficient of resistance of the intervening air is 
so much higher than that of any other part of the 
circuit that an intense localization of resistance 
occurs with corresponding localization of heating 
effect. This is the cause of the intense light. Thus, 
if the carbons are but 1-32 of an inch apart, as in a 
commercial lamp, the resistance may be i l / 2 ohms. 
The poor thermal conductivity of the carbon favors 
the concentration of heat also. The apparent re- 
sistance is too great to be accounted for by the 
ohmic resistance of the interposed air. A kind of 
i thermo-electric effect is produced. The positive 
carbon has a temperature of about 4,000° C. 



MOTION PICTURE ELECTRICITY 109 

(7,232° F.), the negative from 3,000° C. (5,432° 
F.) to 3,500° C. (6,322° F.) This difference of 
temperature produces a counter-electro-motive 
force, which acts to virtually increase the resist- 
ance of the arc. The carbon ends of an arc can 
be projected with the lantern. Globules are seen 
upon them, due to melted silica from the arc of the 
carbon. 

From the foregoing we learn that the electric are is 
simply an effect produced by electric current passing from 
one conductor to another over a gap of comparatively 
high resistance. 

The electric arc may be produced between terminals or 
electrodes of metal, in which case it is called a ''metallic" 
arc. The metallic arc, as compared with the ordinary car- 
bon arc, is greater in length for the same amount of 
power applied, is more likely to flame, due to the 
more rapid volatilization; and the color of the flame 
varies, also depending upon the material used for the 
metal terminals between which the arc is struck. 

The motion picture operator is, for the present at least, 
most interested in the electric arc as produced between 
two carbon points by either direct or alternating current 
as required for the usual form of stereopticon, spotlight 
and picture projector. 

For convenience I will divide the subject into two main 
sections, as follows : 

(1) Direct current projector arc. (2) Alternating 
projector arc. 

THE DIRECT CURRENT ARC 

I will try npw to give you a correct representation of 
what takes place under different conditions when an arc 
is struck and maintained between two carbon electrodes 
with the direct current. 

Experimenters with the electric arc many years ago 
determined that carbon, as it is generally known, is the 
best material for electrodes between which an arc may be 
maintained. It was further determined that for open arc, 



no 



MOTION PICTURE ELECTRICITY 



carbon arc lamps having an automatic feed on constant 
potential direct current circuits, the arc should not be 
longer than required to give a potential drop of 40 to 45 
volts. It was further determined that for best results the 
positive carbon or electrode should be of the cored type 
(which means that the carbon has a hole through its 
center, into which is tightly packed powdered carbon, 
sometimes mixed with chemicals or metallic salts), and 




NEGATIVE CRATER 



ARC MIST 
POSITIVE CRATER 
ARC 



59 



for the negative electrode it was found that a pencil of 
solid carbon, smaller in diameter than the upper carbon, 
on account of the unequal consumption of the two elec- 
trodes, would best serve the purpose. 

We will take for granted that the rules established by 
experimenters during the past twenty-five years, as pre- 
viously referred to, still hold good. 



MOTION PICTURE ELECTRICITY 111 

Fig. 59 illustrates two carbon electrodes between which 
a direct current arc is maintained. The upper electrode 
is a ^-inch soft-cored carbon; the lower is a J^-inch 
solid carbon. 

I have purposely separated the carbon points more than 
would be the case in actual practice with a 40 to 45-volt 
arc; in fact, the distance illustrated is about a third 
greater. I have done this in order to get better oppor- 
tunity to separate the various elements to make the illus- 
tration plainer to you. 

You will note a flame represented by dotted lines ex- 
tending from the lower carbon point around the upper 
carbon. This flame is composed of highly heated gases 
with which are mixed light incandescent particles of car- 
bon, silica, etc., which are constantly carried upwards by 
the induced draft. 

Before going further I want to speak about the "arc 
mist/' because it is a detriment to the arc, in a measure 
acting as a cloud between it and the observer. Experience 
proves that the "arc mist" is greater with impure and 
heavily cored and copper coated carbons. The "arc mist" 
is considerably less between two solid carbons or between 
chemically pure carbons, but unfortunately chemically 
pure carbons are not readily obtained and the resistance 
of the arc with solid carbons would be considerably 
higher, making it necessary to keep the carbon points so 
close together that the negative crater would almost hide 
the positive. This would make the arc inefficient for gen- 
eral purposes, although it might possess a higher individ- 
ual or intrinsic crater efficiency. 

Referring again to Fig. 59, we see there an illustration 
of a normal direct current arc maintained between proper 
carbons, the positive carbon is cored, and the negative 
is solid. The positive crater, it is conceded, furnishes 
more than 75% of the total illumination, and this is very 
important for many purposes, because it centralizes the 
illuminating point in the crater of the positive carbon, 
permitting the crater to be used for projection. The illu- 
mination from the negative crater need not be considered 
at all, and the illumination from the arc proper to a very 



112 



MOTION PICTURE ELECTRICITY 



small value. As a matter of fact, the arc in a direct cur- 
rent projector lamp is really only necessary to maintain 
the high temperature in the positive crater. In view of 
this fact, it becomes .necessary to centralize all possible 
energy at the positive crater and everything possible 
should be done to maintain the carbon separation only 
great enough so that the negative carbon point will not 
interfere with the emission of light from the positive 
crater, and we should also reduce the arc mist to a mini- 
mum by using a solid negative carbon. 

In Fig. 59 the small bubbles or globules, above the 




Fig. 60 Fig. 61 

positive crater and below the negative crater, are intended 
to show the accumulation of impurities in the carbon. 
These generally drop off without being consumed, and 
fall in the bottom of the globe or lamp house, if in a pro- 
jection lamp. 



MOTION PICTURE ELECTRICITY 113 

Fig. 60 illustrates what takes place when two cored 
carbons are used. The arc separation becomes longer for 
the same voltage drop, and the arc mist is almost 50% 
greater, thereby making this form of arc less efficient, and 
more likely to be unsteady on account of draft inter- 
ference. 

Fig. 61 illustrates how a 45-volt open arc looks, main- 
tained between two solid commercial or ordinary carbon 
points. You will note that the points burn flatter, and a 
cap formation is present, on the lower carbon point in 
particular, and the lower carbon point covers almost en- 
tirely the positive crater, which makes this form of arc 
useless for projection purposes. Of course, if a higher 
arc voltage is applied, greater carbon separation is possi- 
ble, but this would make the arc unstable, unless enclosed 
in a small glass globe, which would make it still more un- 
desirable as a projector arc. 

From the foregoing you can make up your mind 
that the best direct current arc for projecting pur- 
poses is formed and maintained between cored posi- 
tive and solid negative carbons, and it is essential 
that these carbons should be as pure and of as high 
grade and as much uniformity of manufacture as 
possible. For direct current it is wrong to use two 
cored carbons, although it is permissible, and it is 
also wrong to use two solid carbons. 

We have found that the direct current open arc is for 
practical purposes easiest maintained between one cored 
positive and one solid negative carbon, and that for auto- 
matically feeding lamps, such as were used some years 
ago and are to-day used for special purposes, including 
automatic stereopticons and certain form's of stage light- 
ing apparatus, automatic searchlights, etc., the arc voltage 
or potential drop across the two carbon points should not 
exceed 45 volts. As a matter of fact, it may vary between 
40 and 45 volts. 

For direct current motion picture projector arc lamps, 
which are, as a general rule, of the hand-feed type, this 
arc voltage is too low. It is more desirable and conven- 



114 MOTION PICTURE ELECTRICITY 

ient to use a higher arc voltage, varying between 50 and 
60 volts, but for best results the arc voltage should not ex- 
ceed 55 volts. 

There are two reasons for the desirability of maintain- 
ing a somewhat higher arc voltage for motion picture arc 
lamps. The first reason may be briefly stated, greater 
flexibility is obtained, making it possible to feed suffi- 
ciently often by hand without losing the arc. In this con- 
nection you may be interested in knowing that : 

It is for general purposes impractical to operate 
an open direct current arc below 38 volts, and it is 
equally impractical to operate such arc at a voltage 
greater than 58, because the hissing point begins at 
about 38 volts and the flaming point of the arc at 
58 volts. 

It is therefore evident that it is not safe to maintain the 
arc voltage with direct current below 40 nor above 58, 
somewhere between these two points can be found the 
most efficient arc voltage for any desired purpose. You 
cannot judge the arc voltage by the distance between the 
carbon points, because the resistance of the arc depends 
upon several factors, including: 

1. The make of carbon used. 

2. The style of carbon (cored or solid). 

3. The number of amperes passing through the arc. 

4. The composition of the core filling of the carbon. 

5. The admittance of oxygen (air) to the arc. 

The only correct way to determine the voltage drop 
across the arc is by a volt meter. 

The second reason for the desirability of a slightly 
longer arc with direct current motion picture projector 
lamps, is that it enables one to separate the two carbon 
points sufficiently, so that the negative carbon will not in- 
terfere with the light rays from the positive crater. You 
should understand that with a low arc voltage and conse- 
quent short arc the negative carbon point would cast a 
shadow, as it were, or be in the direct path of light from 



MOTION PICTURE ELECTRICITY 



115 



the positive crater, materially reducing the amount of 
light available. 

The question of setting the carbons relative to each 
other as well as to the condensing lenses is a matter of 
utmost importance, and here again there are fundamental 
rules which will serve as a guide in securing the most 
practical and efficient carbon setting for any given pur- 
pose. 

It is conceded and understood that the positive 
crater is the only element to be considered in con- 
nection with direct current arc projection. 

CARBON SETTING 

The Right Angle Arc. — It would seem, on this ac- 
count, that a lamp having the crater of the positive car- 
bon facing the condensing lens would be the most effi- 
cient, and this is true, provided it is possible to sufficiently 
localize the positive crater and maintain it in a given posi- 
tion and of uniform intensity. Some of the manufac- 
turers of high-class stereopticons, appreciating the value 




Fig. 62 



of what is called the "right angle" arc lamp, equip their 

lanterns with "right angle" lamps with splendid results. 

Fig. 62 illustrates the relation of the carbons to each 

other in the "right angle" arc lamp. You will note the 



116 MOTION PICTURE ELECTRICITY 

positive crater facing the condenser allows almost all 
available light to become concentrated by the condenser. 
This condition of ideal crater formation could be main- 
tained if no outside interference were present. But there 
are interferences sufficiently great to distort the arc so as 
to make it unstable unless a comparatively small amount 
of current is used and unless the carbons are set and fed 
exactly as they ought to be. 

The setting as in Fig. 62 may be acceptable for stereop- 
ticon work where 10 to 15 amperes will produce the re- 
quired results. 

For motion picture work, however, the requirements 
call for anywhere from 25 to 60 amperes with direct cur- 
rent at the arc, and under these conditions the effect of 
the interferences (which may include magnetic effect and 
drafts) becomes so great that the arc will "stretch," as 
you might term it, burning sometimes on the upper edge 
of the crater and at other times on the lower edge; in 
other words, the arc becomes very unsteady, and as a 
result the temperature of the crater is also subject to sud- 
den variations, which, of course, make the illumination 
on the screen unsatisfactory. I don't mean to say that it 
is impossible to operate a motion picture arc as shown in 
Fig. 62, but it is impractical, and besides the arc lamp re- 
quired is much more complicated and more difficult to 
handle. In view of the foregoing it may be said that, 
while the "right angle" carbon setting for a direct current 
projector lamp as illustrated in Fig. 62 may be the most 
efficient from a theoretical point of view, it is not practi- 
cal for motion picture work. Manufacturers of stereop- 
ticons who are using the "right angle" lamp for stereop- 
ticon work, appreciating this fact, are not using the "right 
angle" lamp for the lower lamp house where the lower 
lamp of a dissolving outfit is to be used in connection with 
a motion picture machine. 

Variable Angle Setting. — While theoretically the 
right angle carbon setting for direct current should give 
the best results possible, in practice, however, it does not 
give good results where more than 20 amperes are used at 
the arc — for motion picture projection. 



MOTION PICTURE ELECTRICITY 117 

This fact, as demonstrated in actual practice, has made 
it necessary to build hand-feed arc lamps for motion pic- 
ture projection, which will permit the setting of the car- 
bons at different angles as most suited to the particular 
condition under consideration. 

Most modern motion picture projection arc lamps are, 
therefore, made with carbon holders adjustable at several 
angles, and the rack, or main body of the lamp — to which 
is attached the carbon holders, is also made adjustable 
relative to the lamp house and the condensing lenses, per- 
mitting the operator to set his carbons at almost any de- 
sired angle in relation to each other, and, at the same time, 
to tilt the whole lamp body to secure the results which he 
may think best. 

While motion picture lamps are constructed to allow 
for these various adjustments, there are fundamental 
rules governing the carbon setting which may serve as 
suggestions to those interested in the art. It is my inten- 
tion, at this point, to impart information on this subject 
which will act as a guide. It is, of course, understood that 
the operator may find it to his advantage to slightly de- 
viate from the main rules, because of possible difference 
in the carbon, the angle at which the machine is set rela- 
tive to the screen, the number of amperes at the arc, etc. 

Fig. 63 illustrates a direct current carbon setting having 
the lower carbon set straight up and down and the upper 
carbon inclining towards it at an angle of about 45 °. This 
carbon setting gives, perhaps, the most satisfactory crater 
formation when used on direct current. The relative 
positions of the two carbons is ideal for maximum crater 
efficiency, and the lower carbon is practically out of the 
way, therefore not interfering with the rays from the 
positive crater. Many operators are using this carbon 
setting with great results, but it takes an expert to handle 
an arc with this setting, because of the fact that the upper 
carbon in burning away naturally moves the crater back- 
wards, away from the lower carbon point. Within fifteen 
minutes' time the upper carbon crater would be much 
behind the point of the lower carbon unless the operator 
in the meantime changes the angle of the upper carbon, 



118 



MOTION PICTURE ELECTRICITY 



or through other means pushes the upper carbon forward, 
or tilts the lower carbon backwards so as to maintain the 
relative positions of the core of the upper carbon and the 
point of the lower carbon the same — as shown in Fig. 6$. 
To say the least, this is a most difficult job, and therefore 
may be considered impractical for general purposes, al- 
though the crater efficiency is very high. 




Fig. 63 



Fig. 64 



In view of the trouble in obtaining constant results with 
the carbon setting as illustrated in Fig. 63, it has been 
universally agreed by operators that the best results with 
direct current are obtained with a soft cored carbon on 
the top and a solid carbon for the bottom, both carbons 
in practically perfect alignment. 

A direct current lamp with the carbons set in perfect 
alignment may be tilted to any degree from the vertical 
position, backwards to an angle of about 45 °, if necessary. 

Operators sometimes find it of advantage to put the 
upper carbon slightly out of line, placing it a 64th or 32d 
of an inch behind the center line of the lower carbon. 
This arrangement in some instances improves the results, 
especially where the machine table tilts forward, as re- 



MOTION PICTURE ELECTRICITY 119 

quired for short projection where the screen is below the 
machine. Under this condition it is not always possible to 
tilt the lamp body sufficiently to get the proper angle on 
the two carbons relative to a vertical line. By putting the 
upper carbon slightly back of the lower one, when the 
lamp has to set straight up and down or tilts forward, the 
positive crater is coaxed forward so as to be better ex- 
posed. 

Hidden Crater. — Inexperienced operators sometimes 
make the mistake of putting the upper carbon ahead of the 
lower, either by accident or on account of not knowing the 
harm of so doing. As a guide and illustration showing 
the results which follow this mistake, I submit Fig. 64, 
from which you will see that the positive crater actually 
forms on the rear side of the positive carbon, which, of 
course, is the side furthest away from the condensing 
lens. More than fifty per cent, of the illumination can be 
lost in this manner. There may be times when it is de- 
sirable to put the upper carbon ahead of the lower as 
shown in Fig. 64. As an illustration, I may mention a 
condition where you have to project a picture on a screen 
considerably higher than the machine, in which case the 
machine-table, lamp house and lamp would be tilted back- 
wards. This, of course, would tilt the carbons backwards 
as well, and, perhaps, too much, allowing the positive 
crater to form too high on the front edge of the carbon, 
thus making the light unsteady. In such case it may be 
allowable to put the upper carbon ahead of the lower. 

Correct D. C. Setting. — Fig. 65 illustrates what I 
consider the correct carbon setting and crater formation 
for perfect and practical direct current motion picture 
projection. The cut is intended to show the carbons in 
perfect alignment, when the lamp is tilted at an angle of 
30 to 45 back of the vertical position with a practically 
horizontal machine table. The carbon setting in Fig. 65 
is thoroughly practical and as efficient as practical results 
will permit. With an arc drop of 50 to 55 volts, splendid 
results are obtained, and by setting the lamp at the proper 
angle an elliptical spot can be secured on the aperture 
plate, which is horizontally oblong, that is, wider than it 



120 



MOTION PICTURE ELECTRICITY 



is high. This is an important point because the picture is 
wider than it is high, making it necessary to have, if pos- 
sible, a spot which is wider than high. One often hears 
the expression "and I got a perfectly round 'light-spot.' ' : 
This refers, of course, to the spot of light on the shutter 
or on a card held in front of the aperture. A round spot 
for motion picture projection is not ideal. The spot which 




Fig, 65 



66 



is wider than it is high is preferable and more efficient, 
and such a spot can be obtained by setting the carbons in 
practically perfect alignment, as shown in Fig. 65, and can 
be controlled by tilting the lamp, or backward and for- 
ward adjustment of the upper carbon. 

Over-prorninent Crater. — Fig. 66 illustrates what 
may be termed a common way of setting carbons for di- 
rect current motion picture projector lamps. In this case, 
the upper carbon is set quite a little back of the center 
line of the lower carbon, and the purpose of this setting 
is to coax the arc forward so as to make a large and con- 
siderably slanting crater on the upper or positive carbon. 



MOTION PICTURE ELECTRICITY 121 

In theory this method of setting may be correct, because 
the crater will be more nearly parallel to the condensing 
lens, but under this condition we are again confronted 
with the difficulty of magnetic and other forces acting 
upon the arc, causing it -to burn on the upper edge of the 
crater most of the time, and at other times, when the arc 
has burned away the upper part of the carbon, the arc 
may go out, or, upon feeding, it will follow the path of 
least resistance, which would, in that case, be the lower 
edge of the crater, making the light on the screen un- 
steady and frequently out of focus. 

For good projection it is necessary to have the crater 
as nearly of uniform intensity over its entire area as pos- 
sible. Operators will find it far better to use a small 
crater of great brilliancy and in a fixed position relative to 
the condensing lens than to use a larger crater of lower 
intensity and necessarily not constant, because of the fact 
that the arc in traveling from one part of the crater to the 
other makes the temperature uneven, and therefore the 
illumination on the screen is not uniform. Besides, the 
arc mist is almost altogether in front of the crater. Very 
little, if any, goes up on the rear side of the positive crater. 

Judgment in Making Settings. — It has been pre- 
viously stated that there are times when it is necessary and 
advisable to put the upper carbon behind the lower, espe- 
cially when the front of the machine table has to be put 
very low or at a great angle for short projection where 
the screen is lower than the machine. 

If you will always keep in mind the fact that the arc, 
being of tremendously high temperature, stimulates a 
considerable draft upwards, due to the difference in tem- 
perature between the air or gases immediately above and 
below the arc, forcing the arc towards the upper edge of 
the positive crater, it will be possible to somewhat limit 
this tendency by putting the upper carbon forward with 
the lower one slightly behind it. As a matter of fact, an 
operator can make the shape of the crater exactly as he 
wants it by simply shifting the upper carbon slightly rela- 
tive to the lower, and I would rather advise a crater for a 



122 MOTION PICTURE ELECTRICITY 

direct current arc like that illustrated in Fig. 65 than one 
like Fig. 66. 

The carbon setting illustrated in Fig. 65 with carbons 
in perfect alignment, with the upper and lower carbons 
of proper proportion, that is, for instance, a ^-inch soft- 
cored carbon on top and a j4 -inch solid carbon on the bot- 
tom, will allow the operator to simply feed his lamp as 
long as the carbons last without making it necessary to re- 
adjust either the lamp or carbons. 

Many operators who do not use the carbon setting as 
shown in Fig. 65 have to frequently push or pull the car- 
bon out of place from one position to another as the lamp 
continues to burn, in order to keep the crater in proper 
shape. All of these troubles are obviated by setting the 
carbons properly to begin with and by using proper car- 
bons. It may be necessary to raise the lamp up or down 
slightly during the run, due to slight difference in the 
relative speed of the consumption of the two carbons, 
but with properly selected carbons even this change is not 
often required. 

The handling of an electric projector lamp for motion 
pictures is not a science. If it were, anyone could operate 
such a lamp after reading publications on the subject or 
after graduating from a college or school. The manipu- 
lation of a projector arc is an art, which has to be ac- 
quired by practical experience with the aid of fundamental 
rules or laws as established by scientific investigation. I 
have met men who were posted from a scientific point of 
view ; in other words, men who had book and school in- 
formation, who could not secure results in practice with a 
projector arc lamp. 

On the other hand, I have seen experienced operators 
who secured far better results on the screen without 
scientific knowledge of the arc. But it is equally true 
that these same operators after receiving technical advice 
and after becoming more acquainted with the various ele- 
ments composing the projector arc, were able to produce 
still more perfect and satisfactory results. 

Operators should not forget that education, as it is 
generally called, on specific subjects is not always in- 



MOTION PICTURE ELECTRICITY 123 

tended to make one qualified to immediately perform the 
operation. Education is rather intended to teach the stu- 
dent how to use certain information and how to make 
himself qualified to perform by experience. 

A doctor or lawyer will attend college for years. Either 
one may pass the college examination, but may fail utterly 
in practice. Therefore the personal equation enters into 
all kinds of work, and that is one reason why some opera- 
tors of motion picture apparatus produce splendid results 
with even inferior devices, whereas others are not able to 
produce satisfactory results at all with the best equip- 
ment. 

Municipal authorities all over the country, on account 
of fire risk, have issued new and drastic rules, and are 
enforcing a system of examination of operators in order 
to make exhibitions safe. Operators should encourage 
examinations of this sort rather than oppose them, because 
it will ultimately weed out the element among them inca- 
pable of properly operating a machine and unable to pro- 
ject a good picture. In the larger cities in particular, 
these examinations are strict. An operator in most cities 
does not get a license as a qualified operator until he has 
passed an examination which may consist of questions 
relative to his knowledge of the electrical part of the 
equipment as well as a full understanding of the motion 
picture machine. Besides, it is in many cases required 
that he shall have had practical experience as assistant to 
a qualified, licensed operator for a considerable period. 
I believe all beginners should be compelled to serve for 
at least six months, working under an experienced opera- 
tor during that time, just the same as apprentices have to 
do in any other trade or profession. It will help to raise 
the standard of the profession ; it will be the means of an 
ultimate increase of the salary of the operators at large, 
because there will be less competition from poor and in- 
experienced men, and managers getting better results will 
be glad to pay higher salaries to operators. 

It is not my intention in this work to dictate to the 
operator. The information which I impart is to guide 
him in securing better results. 



124 



MOTION PICTURE ELECTRICITY 



Settings for Tilted Projectors. — The operator should 
be prepared to meet abnormal conditions where the ma- 
chine-table, lamp house, lamp and machine must be placed 
at a considerable angle above or below the horizontal 
position. The following suggestions may guide the op- 
erator in securing better results. 




In order to make this matter more clear, I submit Fig. 
6j, illustrating a lamp house with lamp tilted backwards 
to project a picture on a screen considerably higher than 
the machine. This arrangement may be necessary in large 
theaters where the operating room is placed below a bal- 
cony, or in the rear on the main floor, or in places where 
the floor does not incline and where it is therefore neces- 
sary to place the curtain above the machine. 

It is evident that with this arrangement the ordinary 
slant of the carbons will be considerably increased by the 
raising of the front of the lamp house, and therefore if 
the carbons are set in perfect alignment, the crater on the 
positive carbon would be forced upwards, making the 
crater long and difficult to control. Under a condition 
of this sort it is advisable to put the center line of the 
upper carbon slightly ahead of the center line of the lower 
carbon, as illustrated in Fig. 64. Please note, however, 
that the crater will not form as in Fig. 64, but, due to the 
lamp and carbons being tilted backwards, it will form 



MOTION PICTURE ELECTRICITY 



125 



higher up, approximately like illustration Fig. 65, which 
is a correct representation of how the crater should look. 
For normal projection where the center of the screen 
is on a level with the projecting lens, the carbon should 
be set as illustrated in Fig. 68, which is practically the 




Fig. 68 



same setting as shown in Fig. 65, w y hich represents the 
proper crater formation for such projection. This setting 
may be considered the best for direct current for general 
purposes. 

There are, however, other conditions to meet. For in- 
stance, where the machine is placed considerably higher 
than the screen, as would be the case in a regular theater 
where it is necessary to place the machine in the front of 
the balcony. Under this condition the machine is much 
higher than the screen, making it necessary to tilt the 
table, lamp house, and machine forward to a considerable 
degree, as illustrated in Fig. 69. Under this condition 
the angle at which the carbons are put, in relation to the 
vertical or plumb line, is considerably decreased ; as a 
matter of fact, the placing of the machine in this position 
may put the carbons in a perfectly vertical position, which, 
of course, is not right for direct current. In order to coax 
the arc forward, it will be necessary to put the upper car- 



126 MOTION PICTURE ELECTRICITY 

bon slightly behind the lower, something like the illustra- 
ti n shown in Fig. 66. 

This matter of adjusting the carbons for different ma- 
hine positions is of considerable importance, and it is 
evident that no universal rule can be applied, but by fol- 
lowing the foregoing suggestions an operator can secure 
the best results possible for any given installation. 




For advertising purposes it is sometimes necessary to 
put the projector in a position where it will show a pic- 
ture immediately below the machine or stereopticon. For 
instance, if it should be required to throw a picture on a 
sidewalk, then the lamp would have to set with the con- 
densing lenses facing down, as illustrated in Fig. 70. 
With the lamp-house set in this position we could utilize 
the right angle carbon setting as illustrated in Fig. 62 to 
good advantage. 

Under other conditions it may be necessary to project 
the picture on the ceiling of a high building, in which case 
the lamp-house would be turned so that the condensers 
would be on top. With the lamp-house set in this posi- 
tion a carbon setting as illustrated in Fig. 71 will perhaps 
serve best. 



MOTION PICTURE ELECTRICITY 



127 




Fig. 70 




Fig. 71 



128 MOTION PICTURE ELECTRICITY 

The conditions referred to, and illustrations Figs, 70 
and 71, are remote and unusual, and could be taken care 
of by using reflecting mirrors, or glass prisms, but I 
thought it best to include them while discussing the di- 
rect current projector arc. 

I would advise operators who may read the foregoing, 
who have at their disposal a direct current supply and a 
projector lamp, to try the various carbon settings referred 
to and observe the results. It will pay any operator to 
practice along these lines, as familiarity with the different 
results obtained will soon make him expert in this matter. 

Taking all of the foregoing into consideration 
it appears that the carbons for a direct current pro- 
jector lamp should be in practically perfect align- 
ment with each other, although in some instances 
the upper carbon may be put slightly forward and 
in other instances slightly back of the lower car- 
bon. It is not advisable to put the two carbons at 
an angle relative to each other, because of the ne- 
cessity of constantly having to readjust the carbons 
in addition to feeding them. 



MOTION PICTURE ELECTRICITY 129 

CHAPTER VII 

Resistance 

THEORY 

BEFORE proceeding with a detailed discussion of the 
subjects under this heading, I wish to present a 
definition of the term "resistance" by Dr. T. 
O'Connor Sloane: 

Resistance is the quality of an electric conductor, in 
virtue of which it opposes the passage of an electric cur- 
rent, causing the disappearance of electro-motive-force if 
a current passes through it, and converting electric energy 
into heat energy in the passage of a current through it. 
If a current passes through a conductor of uniform re- 
sistance there is a uniform fall of potential all along its 
length. If (the conductor is) of uneven resistance, the 
fall in potential varies with the resistance. The fall of 
potential is thus expressed by Daniell : 

In a conductor, say a wire, along which a current is 
steadily and uniformly passing, there is no internal ac- 
cumulation of electricity, no density of internal distribu- 
tion (meaning that the center of a solid wire could be re- 
moved without decreasing the conductivity to any great 
extent. — Ed.), there is, on the other hand, an unequally 
distributed charge of electricity on the surface of the wire, 
which results in a potential diminishing within the wire 
from one end of the wire to the other. 

Resistance varies inversely with the cross section of a 
cylindrical or prismatic conductor, in general with the 
average cross-section of any conductor, and in the same 
sense directly with its true or average or virtual length. 
It varies for different substances, and for different condi- 
tions, as of temperature and pressure for the same sub- 
stance. A rise of temperature in metals increases the re- 
sistance, in some bad conductors, a rise of temperature 



130 MOTION PICTURE ELECTRICITY 

decreases the resistance. Approximately, with the excep- 
tion of iron and mercury, the resistance of a metallic con- 
ductor varies with the absolute temperature. This is very 
roughly approximate. 

Except for resistance, energy would not be expended in 
maintaining a current through a circuit. The resistance of 
a conductor may be supposed to have its seat and cause in 
the jumps from molecule -to molecule, which the current 
has to take in going through it. If so, a current confined 
to a molecule would, if once started, persist because there 
would be no resistance in a molecule. Hence on this 
theory the Amperian currents would require no energy 
for their maintenance and Ampere's theory would become 
a possible truth. 

When metals melt, their resistance suddenly increases. 

Light rays falling on, some substances, notably seleni- 
um, q. v., vary the resistance. 

Longitudinal stretching of a conductor decreases the 
resistance; but increases it with longitudinal compres- 
sion, and increases in iron and diminishes in tin and zinc 
when a transverse stress tends to widen the conductor. 

The term "resistance" is used to express any object or 
conductor used in circuit to develop resistance. 

The foregoing theory and explanation of the word "re- 
sistance" should be studied very carefully in order that 
you may form a clear and thorough understanding of 
what really takes place in an electric conductor under dif- 
ferent conditions when it forms the part of an electric 
circuit. 

Different metals offer different degrees of resistance, 
and it is interesting to know and well to remember that 
all electric conductors of ordinary resistance increase in 
resistance as the temperature is increased. 

You know that whenever an electric current passes 
through a conductor there is a certain amount of loss, due 
to the resistance of the conductor, and that this loss mani- 
fests itself in the shape of heat. 

With this fact established in your mind, you can put 
two and two together and will understand that the more 
current you crowd through a normal or ordinary con- 



MOTION PICTURE ELECTRICITY 131 

ductor, the greater will be the heat generated in such con- 
ductor, and consequently there will also be an increase in 
the resistance of the conductor, andthe tendency or effect 
is to lower the voltage, or potential, at the end of the con- 
ductor. 

You will also find from the foregoing explanation of 
the term "resistance" that there are some bad con- 
ductors which work in the opposite direction, inasmuch 
as the resistance of some such bad conductors will actually 
decrease as the temperature increases, and among such 
bad conductors I may mention, as a practical example, 
the "glower" (a secret mineral composition) as used in 
the Nernst lamp. The ingredients of the Nernst glower 
are not generally known, but are^ made by pressing 
through a die, a dough composed of the oxides of the rare 
earths, mixed with a suitable binding material. The 
porcelain-like string thus formed, is cut, after drying, 
into convenient lengths. It is then baked, and terminals 
are attached by means of which a current of electricity 
may be passed through the glower. For the benefit of 
those who don't know, I will mention that the glower in a 
Nernst lamp, when cold, is an insulator to very high 
voltage electric current, but after it becomes heated by a 
match, alcohol lamp, or by a small red-hot resistance 
wire or heater, it gradually becomes a conductor, 
of high resistance at first; then as the current begins 
to pass through the glower it heats itself, and in a 
few moments its temperature increases so that it glows at 
white heat, and it would melt, and consequently destroy 
itself as the resistance becomes so low at the higher tem- 
perature that it would simply burn itself in two. The ref- 
erence to this glower is very interesting and instructive, 
because its action is just opposite to that of the regular 
resistance wire, which increases in resistance the higher 
the temperature at which it is operated. For this reason 
a Nernst glower, in order to be made practical, has to 
have a "ballast" or steadying or limiting resistance, as 
we may call it, connected in series with the glower. This 
"ballast" is usually made from a material which increases 
rapidly in temperature, and offers a much greater resist- 



132 MOTION PICTURE ELECTRICITY . 

ance when it becomes heated. The glower and the "bal- 
last" resistance act exactly opposite to each other, admit- 
ting, therefore, a steady flow of amperes through the 
"ballast" and glower circuit which is then maintained at 
an automatic balance. 

Now we will use the electric arc in place of the glower. 
Its action, as far as resistance is concerned, is practically 
the same as that of the glower, inasmuch as the resistance 
of the arc when maintained at a constant length, or at a 
given carbon separation, will decrease as the amperes in- 
crease, therefore constantly decreasing the limit of cur- 
rent which can flow between the two carbon points, un- 
less some other element is introduced to counterbalance 
this effect, or, in other words, put a check or limit on the 
current flow. The element which in practice is used for 
this purpose in connection with projector arc lamps, is 
the resistance or rheostat, as it is usually called. For the 
purpose of checking the current in series with the arc, a 
rheostat composed or made of a material which will in- 
crease in resistance as the temperature of the resistance, 
or wire is increased. For a better understanding of the 
foregoing references I refer you to the accompanying il- 
lustrations. 



TO CIRCUIT- 



GLOWER 



rt 






MATCH 



Fig. 72 

Fig. 72 shows a Nernst lamp glower connected to an 
electric circuit with a lighted match below it, the flame of 
which heats the glower so that it becomes a conductor, and 



MOTION PICTURE ELECTRICITY 



133 



Fig. 73 shows the glower in operation, in which condition 
it would last only a second, because the current will crowd 
through it more and more, the hotter it gets, burning it 




Fig. 73 



out as shown in illustration Fig. 74. The correct method 
of operation, in order to prevent the glower from admit- 
ting too much current, is to connect a "ballast" or a re- 



-to circuit - 



Fig. 74 

sistance in series with the glower as illustrated in Fig. 75. 
In this instance the "ballast" is enclosed in a vacuum 
within a glass bulb, and the ballast wire, which is made 
of a material like iron, operates at red heat. 




m/wimm\mw 



Fig. 75 



134 



MOTION PICTURE ELECTRICITY 



Fig. 76 shows almost the duplicate condition of the 
Nernst glower in which the arc between two carbon 



"BALLAST" 

OR STEADYING 

RESISTANCE 




vvwww 



Fig. 76 

points is the equivalent to the glower and the steadying 
resistance or ballast is connected in series with the arc 
the same as required in the Nernst glower. 

PRACTICE 

The subject of the regulating resistance in conjunction 
with the electric arc is so important that in order to fully 
understand its functions the reader should thoroughly 
instill into his mind the following extremely important 
facts before proceeding any further: 

The electric arc introduces a given drop of po- 
tential for a given separation of the carbon points 
and for a specified ampere flow. 

Should the current flowing through the arc be 
decreased in amperes and the carbon separation re- 
remain the same, the potential drop across the arc 
will increase. 

Should the current flowing through the arc be 
increased in amperes and the carbon separation 
remain the same, the potential drop across the arc 
will be decreased. 



MOTION PICTURE ELECTRICITY 135 

From this you will learn that the arc is not self-regulat- 
ing. As a matter of fact its resistance decreases as the 
current is increased, therefore there is practically no limit 
to the amount of amperes which can flow over an arc be- 
tween two carbons connected directly to a constant poten- 
tial circuit, as far as the arc is concerned. 

The direct current projector arc lamp, as has already 
been stated, requires between 45 and 55 volts at the arc. 
On account of the arc not being self-regulating, but 
rather of decreasing resistance with increased flow of 
current, it becomes necessary on regular multiple lighting 
circuits to introduce a resistance of some sort connected 
in series with the arc to limit the current flow. 

The resistance required to limit the current flow and 
to regulate the arc may be called "steadying resistance" 
or "ballast." 

Experience proves that the "ballast" must be 
equal to at least 25 per cent, of the arc voltage. 

If we consider a projecting arc operating with a po- 
tential drop of 50 volts, the necessary potential drop 
across the "steadying resistance" or "ballast" in series 
with the arc must be 25 per cent, of 50 or 12.5 volts, which 
would make the required voltage for the satisfactory op- 
eration of the lamp about 62.5 volts. 

Many attempts have been made to operate a 50-volt arc 
amp on a 50-volt constant potential dynamo without any 
resistance in series with the arc, but this method of opera- 
tion is impossible. 

The lowest voltage constant potential circuit on 
which a direct current projector arc can be main- 
tained in satisfactory operation is 60 volts, but this 
voltage is really too low, and for safe operation it 
is far better to allow a greater margin of voltage 
for the "steadying resistance" or "ballast" ; in fact, 
70 to 75 volts on the line giving 20 to 25 volts drop 
in the "steadying resistance" will give better re- 
sults. 

It is a well-known fact that standard electrical distri- 
bution systems are not available giving 70 to 75 volts, 



136 



MOTION PICTURE ELECTRICITY 



therefore it becomes necessary to operate motion picture 
projector arcs on the standard systems which generally 
supply either no or 220 volts, which, of course, requires 
a greater amount of resistance in series with the arc. 

The steadying resistance must be equal to at least 25 
per cent, of the arc voltage, and also that it is better to 
allow even greater potential drop in the steadying resist- 
ance, going posibly as high as 40 to 50 per cent, for very 
best results. 

Suppose, for the sake of argument, that we allow 5,0 
volts at the arc and 20 volts for the steadying resistance ; 
this makes a total of 70 volts actually required. If we 
have constant potential direct current at 70 volts, we have 
the ideal current supply for a direct current projector arc 
lamp. 



CONSTANT POTENTIAL CIRCUIT 



STEADYING, 

RESISTANCE 

10 VOLTS 




Fig. 77 



The standard lighting circuits, however, as already 
stated, are maintained at r'lo and 220 volts ; therefore we 
must take care of the difference in voltage between 70 
actually required, and the line voltage, which we will say 
is no, making a voltage drop of 40 volts. This extra 
voltage must be taken care of by a resistance offering a 
potential drop of 40 volts at the required amperes, and 
we may call this part of the resistance the "reducing re- 
sistance," because this part of the voltage is not neces- 
sarily required, and must simply be disposed of or used 
up in a resistance and is a dead loss. 



MOTION PICTURE ELECTRICITY 



137 



For 60 Volts. — For a better understanding of the 
foregoing I offer, as an additional explanation, Fig. 77, 
illustrating the application of the electric projector arc to 
a direct current constant potential circuit of minimum, 
allowable line voltage, which as illustrated and referred to 
is 60 volts. 



STEADYING, 

RESISTANCE 

25 VOLTS 



CONSTANT POTENTIAL CIRCUiT 




Fig. 7 l 



For 75 Volts. — Fig. 78 illustrates the application of 
the projector arc to a 75-volt direct current constant po- 
tential circuit, which is the ideal condition of operation 
where the arc is to be controlled by a steadying resistance 
or "ballast." 

For no Volts. — Fig. 79 illustrates the application of 
the projector arc to a standard no-volt constant poten- 
tial circuit, and the illustration shows the steadying re- 
sistance and reducing resistance combined as is the usual 
method of operation where projector arcs are controlled 
by resistance in series with the arc. 

For 220 Volts. — There are, however, other conditions 
to be met where the voltage is greater than no. For in- 
stance, in some cities where only 220 volts can be had for 
the operation of motion picture projector lamps. In 
such a case the reducing resistance combined with the 
steadying resistance or ballast becomes a large unit which 
has to introduce a potential drop of 170 volts, because of 



138 



MOTION PICTURE ELECTRICITY 



the fact that the arc requires only 50 volts. Fig. 80 shows 
the voltage drop in the different sections of the circuit. 
^or 550 Volts. — In amusement parks and some 
towns it is sometimes necessary to operate the projector 
arc on a street railway or power circuit supplying from 
500 to 600 volts. With this high voltage the reducing re- 




Fig. 79 



sistance becomes very large, and as the arc requires the 
same drop, namely, 50 volts, it is evident that about 500 
volts has to be consumed in the reducing and steadying 



d. c. 



220 V. CONSTANT POTENTIAL 




STEADYING AND REDUCING 
RESISTANCES COMBINED -170 VOLTS 

Fig. 80 

resistance. Fig. 81 illustrates such a connection and 
system. 



MOTION PICTURE ELECTRICITY 



139 



Arc Voltage Limit. — It would seem that where the 
line voltage is so high it would be practical to use a 
higher voltage at the arc so as to employ some of the 
energy to increase the illumination instead of wasting it 
in the reducing resistance. Previous information on this 
subject has made you acquainted with the fact that it is 
not practical under any condition to use more than 60 
volts at the arc because at this point the arc begins to 
flame excessively. As a matter of fact, 55 volts is about 



STEADYING 
AND 

REDUCING 
RESISTANCES 

COMBINED 
=■500 VOLTS 




550 V. CONSTANT POTENTIAL 



POWER OR STREET RAILWAY 
CIRCUIT 
\~FUSES 

SWITCH 



ARC 

50 VOLTS 



as high pressure as can practically be used to advantage 
at the arc, and a drop of 50 volts is the ideal pressure at 
which a direct current projector arc should operate. 

The resistance of a projector arc circuit is, in accord- 
ance with the foregoing, composed of three parts : 



First — The drop across the arc, which is usually 
50 volts. 

Second — The drop across the steadying resist- 
ance or ballast in series with the arc, which must 
not be less than 10 volts and need not be more 
than 25 volts. 



140 MOTION PICTURE ELECTRICITY 

Third — The drop across the reducing resistance 
which depends entirely upon the voltage of the 
supply circuit being approximately as follows: 
40 volts on no-volt circuit, 150 volts on 220-volt 
circuit, 480 volts on 550-volt circuit. 

Calculating Resistance. — On pages 20, 21 and 22 are 
given formulae Nos. 1, 2, 3 and 4, by means of which you 
may calculate the amount of ohms required for different 
conditions. Formula No. 4 also permits you to calculate 
the watts expended in the arc as well as the watts ex- 
pended in any portion of the resistance connected in 
series with the arc. 

To refresh your memory, I will offer the following 
problems : 

PROBLEM 1 

Suppose we have a constant potential no-volt direct 
current circuit upon which it is desired to operate a pro- 
jector arc lamp with 30 amperes at the arc — find the total 
number of ohms required for the steadying and reducing 
resistance combined. 

Solution of Problem 1. — Line voltage no — arc 
voltage 50 = 60 volts, which is the potential drop across 
the total resistance in series with the arc. 

E 
Formula No. 2 reads, R = — , or in simplified form, 

C 
resistance in ohms equals 60 volts divided by 30 amperes 
equals 2 ohms. 

PROBLEM 2 

The same as Problem No. 1, but in this case the line 
voltage is 220. 

Solution of Problem 2. — Line voltage 220 — arc 
voltage 50 = 170 volts, which is the total drop in the 
steadying and reducing resistance, in series with the arc. 
Using again Formula No. 2 (page 21), we find resistance 
in ohms equals 170 divided by 30 amperes, 5^3 ohms. 



MOTION PICTURE ELECTRICITY 141 

PROBLEM 3 

Find the number of watts required per hour for a 
30-ampere projector arc lamp on no-volt direct current 
circuit. 

Solution of Problem 3. — Total line voltage no, total 
amperes 30, Formula No. 4 reads, W ±= C X E ; in other 
words, watts equal 30 amperes times no volts or 3,300 
watts or 3.3 kilowatts per hour. 

PROBLEM 4 

Find the number of watts expended in the arc (only) of 
a projector lamp operating at 50 volts with a current flow 
of 30 amperes. 

Solution of Problem 4. — Watts = 30 amperes X 50 
volts or 1,500 watts, or 1.5 kilowatts per hour. 

PROBLEM 5 

Find the number of watts lost in the resistance con- 
nected in series with a 50-volt 30-ampere projector arc 
lamp on no-volt direct current circuit. 

Solution of Problem 5. — The voltage drop across the 
total resistance in series with a direct current projector 
arc, on no volts, we have previously found to be 60; 
using again Formula No. 4, we find that watts expended 
equal 30 amperes X 60 volts, which equals 1,800 watts 
or 1.8 kilowatts per hour. 

This last example is interesting in comparison because 
it proves to you that of the total 3.3 kilowatts required 
from the line only 1.5 kilowatts is made use of at the arc; 
the balance, which is the greater part representing the 
1.8 kilowatts, is lost in the shape of heat in the resistance. 

There are several methods which can be employed for 
the purpose of reducing the line voltage to the proper 
amount required for the control of a projector arc lamp 
on direct current, and we will discuss, in the chapters 
following, these various methods. 

Considering previous references to the direct current 
projector arc, we have established the fact that 

the electric arc does not put a limit on the amount 
of current which can be carried by it. As a matter 



142 MOTION PICTURE ELECTRICITY 

of fact, the resistance of the arc decreases as the 

temperature increases. 
Therefore, permitting a continually increasing amount 
of amperes to flow over the arc, up to the capacity limit 
of the conductors and generators which supply the cur- 
rent. We have determined that the direct current pro- 
jector arc is most efficient with a potential drop of about 
50 volts, and that, in order to limit or regulate the amount 
of current flowing across the arc, a given amount of bal- 
last or steadying resistance must be connected in series 
with the arc. The potential drop across this ballast or 
steadying resistance must be at least 25 per cent, of the 
arc voltage, which would make the minimum voltage 
upon which a direct current projector arc may be op- 
erated, between 60 and 65 volts. We know that the po- 
tential — usually supplied by the ordinary electric systems 
— varies between 100 and 60 volts, and we have also cal- 
culated the various amounts of resistance required in se- 
ries with projector arc lamps on different voltages. 



MOTION PICTURE ELECTRICITY 143 



CHAPTER VIII 

The Rheostat 

THE RHEOSTAT is a device to be connected in 
series with an electric arc, and its purpose is : 

First : To reduce the line voltage. 

Second: To introduce the necessary steadying 
effect, in order that the arc may be maintained with 
normal current flow. 

The rheostat is usually composed of a wire, mounted 
on an insulating frame, beginning at one terminal of the 
rheostat, the other end being connected to a second ter- 
minal. There are many different kinds of rheostats, em- 
ploying many kinds of wire, made up in hundreds of 
ways, to suit the ideas of each individual manufacturer. 

There are four essential points, however, which govern 
the designer of rheostats : 

First: The temperature of the resistance unit 
must not be so high as to cause excessive depre- 
ciation of the resistance medium or wire. 

Second: The construction must be such, that 
continued expansion and contraction will not loosen 
the clamps which hold the various sections of the 
resistance unit in contact with each other. 

Third : There should be a fairly large space be- 
tween the resistance unit, and the metal parts, 
which form the frame and the metal casing sur- 
rounding the unit so as to prevent excessive heat- 
ing of the external metal parts. 

Fourth : Only porcelain, mica and asbestos or 
other similar non-combustible materials should be 
used for the insulation of the various supports and 
terminals in a rheostat. 

The resistance for an arc lamp must be of the kind 
which will increase with an increase of current flow, and 



144 



MOTION PICTURE ELECTRICITY 



consequent temperature rise. It has been found that iron 
or steel wire possess this quality. For practical pur- 
poses, however, the pure iron or steel wire, is not of suffi- 
ciently high resistance; therefore, it is customary to use 
a wire made from a special alloy, composed of steel and 
nickel which increases the resistance to a considerable 
extent, thereby reducing the length of wire required, 
which at the same time, of course, reduces the over all 
dimensions of the frame and rheostat casing. 




For the highest class of rheostats, a special wire made 
from an alloy composed mainly of nickel and copper is 
sometimes used. The object in using nickel copper wire 
is to prevent rust, especially where the rheostat is used 
outdoors, or transported from place to place where it 
would be likely to be subjected to severe weather condi- 
tions, and consequent unusual and rapid temperature 
change. 



MOTION PICTURE ELECTRICITY 



145 



Non- Adjustable Type. — Fig. 82 illustrates a rheostat 
having the resistance unit composed of a resistance wire 
mounted in zigzag form on small insulating buttons, sup- 
ported by a suitable metal frame, enclosed in a ventilated 
metal case. The illustration shows the beginning and 
end of the resistance wire attached to proper binding posts 
or terminals supported on an insulating block or base. 
The metal casing is generally made of perforated sheet- 
iron, aluminum or brass and this cover or protecting case 
must entirely enclose the resistance unit and terminals and 




Fig. 83 



suitable openings with proper bushings should be pro- 
vided in the metal case, through which the asbestos cov- 
ered copper cables may enter for making connection with 
the binding posts. It is evident with such a rheostat as 
described in the illustration, if the proper size wire is 
used, would be absolutely fireproof and almost indestruct- 
ible and the great advantage of this particular type of 



146 MOTION PICTURE ELECTRICITY 

rheostat is due to the fact that the resistance wire is con- 
tinuous from one end to the other without a break. 

Fig. 83 illustrates a similar type of rheostat, which is, 
however, somewhat simpler in construction, in that it re- 
quires a lesser number of insulating supports which is ac- 
complished by winding the resistance wire on an arbor in 
the form of a spiral, so as to make the resistance unit 
more compact. This form of resistance unit can, of 
course, not be operated at as high a temperature as the 
design illustrated in Fig. 82 on account of the possible sag- 
ging of the spirals, as the wire loses its temper when 
heated excessively. The spiral form of resistance is, how- 
ever, the type generally used and if not overloaded gives 
excellent satisfaction. Fig. 83 shows also a continuous 
wire without a break. For convenience of manufacture, 
a resistance unit is generally made in several short spirals 
which are connected together at each end so as to form 
a continuous series circuit — from one end to the other. 
This form of construction, in sections, is not as good as 
the continuous construction illustrated in Fig. 83, on ac- 
count of the possibility of loose contact between some of 
the units, but if carefully designed and constructed, the 
possibility of trouble on this account can be almost en- 
tirely eliminated. 

For the control of street railway motors, and for the 
field control of large generators, there has been used, for 
some years, a rheostat made up from cast-iron grids or 
plates, of zigzag form which are mounted so as to furnish 
a continuous strip of cast-iron in series with the electric 
circuit. Where the rheostat is not subjected to excessive 
vibration or jar, this form of construction is very desir- 
able and satisfactory. The "grid" type resistance is now 
also used for the control of projector arc lamps, and is 
sometimes preferred to the wire rheostat because it will 
stand a heavier or greater overload, and is of very solid 
construction. The grid type rheostat should be examined 
at frequent intervals in order to make sure that the bolts 
or clamps, which connect the resistance plates together, 
have not become loosened — due to frequent expansions 
and contraction. 



MOTION PICTURE ELECTRICITY 



147 



The rheostats so far mentioned, are of the non-adjust- 
able type. Under certain conditions it is necessary to use 
an adjustable rheostat, in which case, a switch arm, mak- 
ing contact with a number of buttons connected to differ- 
ent sections of the rheostat has to be used. Fig. 84 illus- 
trates an adjustable rheostat in diagrammatic form. 

RESISTANCE UNIT 




Fig. 84 



Adjustable Type. — Fig. 84 illustrates the principle 
on which an adjustable rheostat works. By referring to 
the diagram, it will be seen that the entire resistance unit, 
which may be of any type desired, is stretched out or 
mounted in suitable manner. The beginning end may be 
attached to one line wire, the other end to a contact but- 
ton or contact plate, which forms the last step of an ad- 
justable or dial switch. Several additional buttons may 
be provided, each one being connected with some inter- 
mediate point on the resistance unit. The distance be- 
tween these points determines the difference in voltage 
drop between each contact button on the dial switch 
which, of course, increases the flow of amperes through 
the rheostat as the dial switch is swung to the left, cutting 
out sections of the resistance unit in series with the arc. 
One lead from the arc lamp is connected to the lever of 
the dial switch, and the other arc lamp lead, not illustrated, 
is connected to the second line wire, forming a complete 



148 



MOTION PICTURE ELECTRICITY 



series circuit from the first line wire through whatever 
portion of the rheostat may be in series with the dial 
switch, through the arc lamp back to the line. 

Fig. 84 shows the simplest form of adjustable rheostat 
and the cheapest to manufacture. For special purposes, 
however, more elaborate adjustable rheostats can be made 
and as a simple illustration, I call your attention to Fig. 
85, in which the rheostat is composed of several independ- 



TO LINE 




Fig. 85 



ent spiral resistance units all connected together at the 
top, but the lower ends are connected to independent sin- 
gle pole switches. The switches are, however, connected 
together at the lower end. An examination of this ar- 
rangement will prove to you that if the connections are 
made as illustrated in Fig. 85, and all switches are closed, 
the rheostat offers the lowest amount of resistance and 
allows the greatest number of amperes to flow over the 
arc because the entire number of resistance units are 
connected in parallel or multiple. 

Let us assume, as an example, that each one of the re- 
sistance spirals allows a current flow of 10 amperes with 



MOTION PICTURE ELECTRICITY 149 

a given line voltage and that the potential drop at the arc 
is just 50 volts, then the current flow over the arc will be 
as follows : 

With Switch No. 1 closed ,10 amperes 

With 1 and 2 closed 20 amperes 

With 1, 2 and 3 closed 30 amperes 

With i, 2, 3 and 4 closed 40 amperes 

With all switches closed 60 amperes 

You will appreciate the great advantage of rheostats 
constructed on this plan because each resistance unit is 
absolutely independent of any of the others, and in case 
one unit should become disabled, it does not prevent you 
from operating the rheostat, although with slightly lower 
current flow. 

Rheostats built on the principle illustrated in Fig. 85, 
can also be made in sub-divided sections so as to permit 
each half to be connected in series for 220 volts and in 
parallel for no volts. 

It is also evident that any one of the resistance units 
illustrated in Fig. 85, can be made in any desired capac- 
ity. For instance: 

Unit No. 1 can be made to allow a current flow 

of 20 amperes, 
Unit No. 2, 10 amperes, 
Unit No. 3, 5 amperes, 
Unit No. 4, 2% amperes, 
Unit No. 5, 1 ampere, 

giving a most perfect control of the current flow through 
the arc. 

If all switches are open and you close switch No. 3, 
the arc would operate at 5 amperes. If switch No. 2 is 
closed and all other switches open, the current flow will 
be 10 amperes. If switches 2 and 3 are closed, the cur- 
rent flow will be 15 amperes. If we also close switch 
No. 1, the current flow will be 35 amperes and so on, de- 
pending upon the number of switches that are closed. 

For regular motion picture projector arc lamps, the 
type of rheostat, illustrated in Fig. 85, is not necessary, 
because the voltage supply is generally constant and op- 



150 



MOTION PICTURE ELECTRICITY 



erating conditions do not vary to any great extent. A 
fixed non-adjustable rheostat is always preferable where 
an adjustable type is not necessary. 

For the traveling show, however, an adjustable rhe- 
ostat constructed along the lines as illustrated in Fig. 85 
is very desirable, especially if the design is elaborate as 
in Fig. 86, which shows a complete interchangeable unit 
for no or 220- volt line having any ampere output desired, 
depending upon the size of the different resistance units. 
When using the design shown in Fig. 86, it is important 



TO 110 OR 220 V. LINE 

4 5 




that all resistance units be made to pass the same number 
of amperes unless the operator practices care in closing 
only corresponding switches on each side of the rheostat, 
in which case it is permissible to make the resistance 
units of different degrees of resistance and capacity to 
allow for a varying flow of amperes. 

In explanation of the foregoing statement, I may say 
that if, in Fig.' 86, resistance No. 1 is of the same capacity 
as No. 6, these two switches may be closed, allowing the 
two resistance units to operate either in series or parallel, 
depending upon the position of the controlling switch. If 
the controlling switch is in the upper position as shown, 
the resistance units will operate in parallel, which is more 
clearly illustrated in Fig. 87. 

If the controlling switch is closed in the lower position 



MOTION PICTURE ELECTRICITY 



151 



the resistance units will operate in series as is more clearly 
illustrated in Fig. 88. 

Again referring to the operation of this form of rhe- 
ostat with unequal resistance units I may say that if re- 
sistance No. 3 in Fig. 86 is made for 5 amperes, and re- 
sistance unit No. 10 is made for only one ampere, it would 
not do to leave only these two switches closed when the 
rheostat is to be used in series on 220-volt line as the two 
units on opposite sides must be of the same ampere ca- 
pacity, and therefore, if No. 8 resistance unit is of 5 am- 




Fig. 87 



Fig. 88 



pere capacity it should always be in series with No. 3, 
which is also of 5 ampere capacity. 

METHODS OF CONNECTING 



When using the term "rheostat" we naturally refer to 
a resistance box, within which is contained one or more 
resistance units of either the non-adjustable or adjustable 
type. On page 148 you were advised how, within one re- 
sistance box or rheostat, several resistance units of like 
or unlike capacity can be combined and by the manipula- 
tion of switches, almost any degree of current strength 
can be obtained for either series or parallel (or, as it is 
also called, multiple) connection. 

Before proceeding further I want to state that the same 
rheostat may be used for either a. c. or d. c, but it must 
be remembered that a given rheostat will pass from ten 



152 



MOTION PICTURE ELECTRICITY 



to twenty per cent, more amperes when used on a. c. This 
is providing the line voltage is the same for both currents. 
The increased current is due to the fact that the a. c. arc 
gives best results at 35 volts as compared with the d. c. 
arc at 50 volts. 

Single Multiple. — Fig. 89 is a diagrammatic illustra- 
tion of an ordinary 25-ampere rheostat for a 50-volt pro- 
jector arc lamp operating on no-volt line. This rheostat 



60 V 


RHEOSTAT 
FOR 

25 AM?. 


11 

WITH 


V. LINE 

50 VOLT ARC 




TO 110 V. 
LINE 



/^■n VOLT A< 



Fig. 89 



-© 



NO.1 



NO. 2 
@- 




Fig. 90 



is of the same design and construction as illustration Fig. 
83, and is the type generally furnished with motion pic- 
ture machines. 

Double Multiple. — There are conditions under which 
it is necessary to have a greater amount of amperes. For 
instance, where alternating current is used, because of 
the fact that with the a. c. arc the upper and lower carbon 
craters are both of the same intensity, or light giving 
quality and, as a general rule, with the ordinary angle 
carbon setting, only one of the craters cam be focused. 
Also, for long projection, that is to say, where the dis- 
tance is more than 80 feet or where a picture is consider- 
ably larger than 12 feet wide, and in other places where 
a brilliant picture is required, it becomes necessary to 
increase the current flow at the arc. The increase in am- 
peres at the arc can, of course, be had by installing a spe- 



MOTION PICTURE ELECTRICITY 153 

cially constructed rheostat to pass a greater amount of 
current. There are, however, cases where a special rhe- 
ostat is not available, and under such conditions it is 
possible to combine two or more ordinary rheostats, which 
may be connected in parallel or multiple. Fig. 90 shows 
two ordinary 25-ampere, no-volt rheostats connected in 
multiple for the control of one projector arc lamp, which 
under this condition will operate with about 50 amperes 
at the arc. 

It is evident, of course, that it is possible to use 110- 
volt rheostats of different amperes in parallel or multiple, 
as illustrated in Fig. 90, and as an illustration, I may say, 
that rheostat No. 1 might be of 25 amperes capacity, and 
rheostat No. 2 of 10 amperes capacity, under which con- 
dition the arc would not receive 50 amperes, but the sum 
of 25 and 10, which is 35 amperes. Anyone interested in 
the art can understand how almost any combination can 
be obtained, and all that is necessary to keep in mind is the 
fact that whenever rheostats are used in a parallel or mul- 
tiple combination, each individual rheostat must be con- 
structed for the operation of a projector arc lamp on no 
volts. In other words, the potential drop across each 
rheostat, with the specified amount of amperes which it 
will safely carry, must be the difference between the line 
voltage, which is no and the arc voltage which should 
average 50, leaving a balance of 60 volts as representing 
the potential drop across each rheostat. 

Triple Multiple. — It may, under some conditions be 
necessary to use as much as 75 amperes at the arc which, 
by the way, is customary in several countries where the 
projection is long, the pictures are large and where ex- 
tremely brilliant pictures are required. In cases of this 
sort, three ordinary 25-ampere rheostats may be con- 
nected in multiple if one specially constructed 75-ampere 
rheostat is not available. Fig. 91 shows such a connection. 

Where 220-volt circuits are to be considered, the same 
arrangement, as illustrated in Figs. 89, 90, 91 can be 
applied, providing, of course, that each individual rhe- 
ostat is made for operation on 220 volts instead of for 
no volts as illustrated. 



154 



MOTION PICTURE ELECTRICITY 



Series for 220 Volts. — Where specially constructed, 
220-volt rheostats are not at hand, ordinary no-volt rhe- 
ostats may be combined to answer the purpose by prop- 
erly connecting them. It will not do, as a general rule, 
to connect two ordinary no-volt rheostats in series for 
220 volts — excepting in case of an emergency, because 
if the rheostats are constructed for 25 amperes and each 
one offers a potential drop of 60 volts, together with the 



TO 110 V. 
LINE 



©- 



--% 



%■ 



Fig. 91 



TO 220 V. 
LINE 



® 



80 V. 

25 AMP. 



© 



60 V. 
25 AMP. 

® 



® 

60 V. 



®- 



Fig. 92 



arc offering a drop of 50 volts, the total drop across the 
two rheostats in series, and the arc, equals only 170 volts, 
whereas, the line is 220, which leaves a balance of 50 
volts higher potential than ordinarily considered safe for 
two such rheostats controlling one 50-volt arc> The re- 
sult is an increase of current, unless anotHer rheostat 
offering an additional drop of 50 volts is introduced in 
series with the two other rheostats, and the arc, as illus- 
trated in Fig. 92. 

Fig. 92 shows a slight discrepancy as compared with 
the above figures, because for convenience I use three 
no-volt 25-ampere rheostats, each one offering a drop 



MOTION PICTURE ELECTRICITY 



155 



of 60 volts, whereas one should have a small part cut out, 
so as to offer a drop of only 50 volts, in order to make 
the circuit balance at exactly 25 amperes, but in practice 
this difference is not large enough to be of much account. 
However, those who wish to maintain the arc at full 25 
amperes with 50 volts, may cut out about 20 per cent, of 
the resistance units in one of the rheostats. 



+ 











TO 220 V. 




LINE 


— »- 


^ 


1 












<A> 


(§> 


60 V. 




60 V. 


25 AMP. 




25 AMP. 


<g> 














r tl 










4 


b 






60 V. 




60 VOLTS 


25 AMP. 




25 AMP. 


a 


P 




(?) 












t 




t 














i 


9 


4 


\) 


60 V. 




60 VOLTS 


25 AMP. 




25 AMP. 
® 





















T ' — 



\ 



Fig. 93 



Multiple Series for 220 Volts. — Fig. 93 illustrates six 
ordinary no-volt, 25-ampere rheostats connected, in 
multiple-series where 50 amperes at the arc is necessary 
when operating on 220-volt line, and where only ordinary 
no-volt rheostats are obtainable. 

As a guide, I show the flow of current by the small 
arrows on the illustrations, giving a clearer idea of just 
how the current flows through the different sections of 
the circuit. 

It is 'well to remember that it does not make a particle 
pf difference on which side of the line the rheostat is con- 



156 MOTION PICTURE ELECTRICITY 

nected. The effect is just the same whether rheostats 
are on the positive or negative sides of a direct current 
system, and it does not make any difference whether the 
rheostat is connected in series with the upper or lower 
carbon of the arc lamp as long as it is in series with the 
circuit at some point. 

It is also well to remember that almost any rheostat 
offers a lower resistance when it is cold than when it be- 
comes heated, and the increase in resistance of the aver- 
age rheostat is about 15 to 20 per cent. This means that 
if you start the arc lamp and measure the amperes, the 
ampere meter may read 30, but within 5 or 10 minutes' 
time when the resistance units become heated, the ampere 
meter would show anywhere from two to five amperes 
less current flow. The above statement is based on the 
average commercial rheostat using iron or nickel-steel or 
german-silver wire. Rheostats can be constructed to 
give a constant voltage drop, but as a general rule, the 
resistance increases and consequently the voltage will also 
increase across the rheostat, and as a result thereof, the 
current in amperes at the arc will decrease as the tem- 
perature of the rheostat increases. 

SPECIAL TYPES 

Up to this point we have considered only the ordinary 
means for the control of direct current motion picture arc 
lamps, and we have found that a resistance unit, usually 
called a rheostat, can be and is generally used for this 
purpose. There are, however, other means and methods 
which can be employed for the control of direct current 
motion picture projector arcs, some of which are prac- 
tical, and others impractical, although any of the follow- 
ing systems of control will work. 

Suppose we have a 50-volt 25-ampere projector arc 
lamp to be operated upon a no-volt direct current con- 
stant potential system. We have found that in a case of 
this kind it is necessary to introduce in series with the 
arc a resistance unit, or a rheostat, having a potential 
drop of 60 volts when 25 amperes is flowing through the 
circuit. It is evident that any other form of resistance 
offering a drop of 60 volts can be used. 



MOTION PICTURE ELECTRICITY 157 

Incandescent Lamp Type. — As an illustration of this, 
I submit Fig. 94, which shows a bank of incandescent 
lamps connected to operate in multiple with each other 
and in series with the arc. In Fig. 94, there is illustrated 
a properly fused line switch connected to a no-volt cir- 
cuit, together with fifty 120-volt one ampere incandescent 
lamps — in other words, about the same as the regular 
32-candlepower incandescent carbon filament lamps. 
The lamps are connected in multiple and one of the ter- 
minals is connected to the line, the other terminal to one 
of the carbon holders of a projector arc lamp. The other 
terminal is connected directly to the second carbon holder, 
making a complete circuit through the arc and through 
each individual one of the 50 incandescent lamp filaments. 

When this system is in operation with the arc at 50 
volts, it is evident that the lamps receive only 60 volts. 
When a 120-volt 1 ampere lamp is operating on only 6o 
volts, the amperage taken by the lamp is approximately 
50 per cent, or y 2 ampere, therefore, the arc will be regu- 
lated by the incandescent lamps and will receive approxi- 
mately y 2 ampere through each lamp, making a total of 
25 amperes at the arc with 50 lamps connected as 
illustrated. 

This method of operation is perfectly safe, providing 
the main line is wired, fused and switched for 50 amperes, 
which is the total capacity of the bank of lamps when 
operating directly on no-volt circuit, in which case the 
lamps were installed in the regular way and the arc used 
course, not be possible unless the carbons are held to- 
gether, and this would extinguish the arc. The system 
is exactly the same as if fifty ordinary 32-candlepower 
lamps were installed in the regular way and the arc used 
as a switch, or as a dimmer for the incandescent lamps. 
When the arc is maintained at 50 volts, the incandescent 
lamps receive only 60 volts, giving a correspondingly 
lower candlepower, in fact the filament will slightly more 
than glow. 

Attempts have been made, and some patents have been 
taken out on the combination of arc lamps with incan- 
descent lamps as rheostats, the object being to secure il- 



158 



MOTION PICTURE ELECTRICITY 




MOTION PICTURE ELECTRICITY 159 

lumination from the incandescent lamps as well as from 
the arc, thus utilizing some of the usual waste in the rhe- 
ostat with direct-current systems, but if any great degree 
of illumination is to be had from the incandescent lamps, 
they would necessarily have to be made for lower voltage, 
and the exact correct amount would be 6o-volt lamps, each 
one allowing about one ampere to flow, in which case 25 
lamps only would be required. The great danger in this 
case would be that at the instant the carbons are put to- 
gether to strike the arc, the 60-volt lamps would for an 
instant receive no volts, or 50 volts more than they are 
intended for, which would be likely to burn them out. 

Considering this scheme of regulating the arc from all 
points of view, there appears to be no practical advantage 
in its application, as under the very best conditions the 
amount of light received from the incandescent lamps 
would be very small and could only be used in some par- 
ticular instances for perhaps a novel advertising scheme, 
but the system is not recommended. At the same time I 
wanted to call it to your attention as being one of the 
possible means for regulating an electric arc, and it may 
have its application in certain specified cases, but should 
be placed in the list of the impractical controlling devices. 

Storage Battery Type. — Another method for reduc-~ 
ing the line voltage to that required for a projector arc 
with direct current is to install a storage battery which 
may be connected in series, but in opposition to the cur- 
rent flowing through the arc in such a manner that the 
battery will receive a charge at the rate of 25 amperes 
with a potential drop of about 60 volts when operated in 
series with a 50-volt arc on a 1 10- volt direct current con- 
stant potential system. 

Fig. 95 illustrates such an installation, and for the pur- 
pose there would be required about 25 cells of storage 
battery, each one of a capacity to stand a continuous 
charge of 25 amperes. You will note that I have illus- 
trated a small ballast, or steadying resistance, in series 
with the arc with this system. This is to prevent exces- 
sive flow of current through the battery at the time the 
arc is struck, and also to assist the regulation. 



160 



MOTION PICTURE ELECTRICITY 



This method of regulation may be of some advantage 
in cases where the electric energy stored in the battery 
can be made use of for some other purpose. As an illus- 
tration, I may mention that the energy from the storage 
battery could be made use of for the operation of vacuum 
cleaning motors, or for slot machines — in fact for any 
purpose where a low voltage direct current is of advan- 
tage. It is understood that this energy received from the 



110 V. D.C. 



25 AMP. 
STORAGE 
BATTERY 



BALLAST OR 
STEADYING 
RESISTANCE 




storage battery is only about 50 or 60 per cent, of the 
amount put in, but still it is a saving of at least 50 per 
cent, of the amount generally wasted in the rheostat. It 
cannot be said that this method of control is practical, 
although it may have its application in certain places and 
under conditions suitable to it, and it may be of advan- 
tage to some readers to know that it is possible to use it. 
This system may, however, be placed in the list with 
other impractical controlling devices for the direct current 
projector arc. 



MOTION PICTURE ELECTRICITY 



161 



Water Type. — -Where a resistance unit of the ordi- 
nary rheostat type is not available, it is possible to manu- 
facture for quick use a resistance unit which is composed 
of a barrel with a metal plate at the bottom to which is 
attached by means of a rubber covered cable one terminal 
of the circuit, and a second metal plate movable up and 
down, to which is attached another wire to be connected 

TO LINE 




Fig. '96 



in series with the arc lamp and the other terminal of the 
line. When such a device is filled with salt water, it will 
allow current to pass through the circuit. The strength 
of current will depend upon the distance between the two 
metal plates and upon the amount of salt put in the water. 
Such an outfit is usually called a ''water" rheostat and is 
illustrated in Fig. 96. The lower you set the upper plate, 



162 MOTION PICTURE ELECTRICITY 

that is, the closer it is to the lower plate, the greater the 
amount of current that will flow ; and the more salt there 
is in the water, the lower will be the resistance of the 
water, and consequently more current will flow. Water 
rheostats are very useful, especially for the higher volt- 
ages, in case of an emergency, and operate fairly satis- 
factorily, although the water becomes heated in a short 
time and such rheostats require more or less attention. 

There are also other methods belonging to the imprac- 
tical list which I do not deem it necessary to refer to, as 
they would be of no practical value to the general reader. 



MOTION PICTURE ELECTRICITY 163 

CHAPTER IX 

D. C. Motor-Generators 

AUTOMATIC AND CURRENT - SAVING DE- 
VICES FOR THE CONTROL OF DIRECT 
CURRENT PROJECTOR ARC LAMPS 

IT has been previously stated that the direct current 
projector arc will operate with best results at a po- 
tential drop varying between 50 and 55 volts, and 
furthermore that it is necessary to connect in series with 
the line and the arc a ballast, or steadying resistance, 
across which there must be a potential drop of about 10 
to 25 volts for perfect arc regulation. 

We have come to the conclusion that a constant poten- 
tial pressure of 60 volts is the very lowest voltage with 
which a direct current hand fed projector arc can be 
properly maintained, and we have also established the 
fact that it is better to have more than 60 volts ; in fact 
a good average would be 70 volts. Assuming that 70 
volts constant potential current is required, it is obvious 
that in view of the fact that the electric companies supply 
not less than no volts, there is a loss of 40 volts usually 
wasted in a rheostat in series with the arc and the line. 
This extra 40 volts is of absolutely no use, but is simply 
made necessary on account of the excessive line voltage 
delivered by the electric company. It is not practical for 
the electric lighting company to reduce the voltage of its 
system in order to accommodate a few users of motion 
picture and stereopticon lamps, spot lights, etc., therefore, 
it becomes necessary for the exhibitor who wishes to 
economize on his electric current bill and to secure the 
best results to install a device which will reduce the volt- 
age from no to that required by the arc for the direct 
current projector lamp. 

To accomplish this voltage reduction, it is possible to 



164 



MOTION PICTURE ELECTRICITY 



install a motor made to operate on whatever the line 
voltage may be. This motor should be used for driving 
an electric generator wound for the proper voltage, which 
in the case above specified would be about 70 volts. With 
such motor generator installation changing the line volt- 
age to 70 volts there will, of course, be required a small 
balast, introducing about 15 to 20 volts potential drop 
in series with the 70-volt generator and the arc, which is 
necessary in order to give proper regulation to the arc, 
as has been described. 



70 VOLTS D.C. 





20 VOLT, , 60 V. 
BALLASTS. ARC 7\ 

- ob f X 

STEADYING I 1 &>* 

RESISTANCE \^*^ 



Fig. 97 



Fig. 97 illustrates in diagrammatic form a motor gen- 
erator installation of this kind. On the left is shown the 
motor, which is an ordinary electric motor of any kind. 
This may be wound for no, 220 or 550 volts as the case 
may require. In the illustration the motor is shown di- 
rectly connected to an electric generator mounted on the 
right hand side of the base. This electric generator is 
somewhat special in that it is made for low voltage, that 
is, to deliver somewhere between 60 and 70 volts, as the 
particular requirements of any given installation may de- 
mand. The carbons are illustrated with the arc at 50 
volts, in series wiih which there is connected a ballast, 
or steadying resistance, offering a drop of about 20 volts. 

A motor generator set of this kind which is nothing 
more than an ordinary motor generator outfit, is com- 
paratively inefficient when we consider that not more 
than 25 to 40 amperes will be required for the arc. As 
a matter of fact, the losses in the motor and the generator 
almost equal the loss in an ordinary rheostat which would 



MOTION PICTURE ELECTRICITY 



165 



be used to reduce the voltage. The saving would not 
perhaps amount to more than 15 or 20 per cent, at the 
most, and as such machines are very expensive, it is 
doubtful if they would be practical, excepting on the 
higher voltages, ranging from 200 to 600. 

The author has, however, designed a line of voltage re- 
ducers for direct current, which, while in appearance re- 



CURRENT AT ARC 
ADJUSTABLE 




Fiat. 98 



semble the ordinary motor generator machine, are rad- 
ically different in both design and construction. Illus- 
tration Fig. 98 is a correct representation of such a direct 
current arc regulator and economizer. The most strik- 
ing feature of this machine as illustrated in Fig. 98 is 
that no ballast, or steadying resistance, is required in se- 
ries with the arc. The machine is absolutely automatic, 
and the guaranteed saving is 40 to 50 per cent, on no 
volts, 65 to 70 per cent, on 220 volts, and 85 to 90 per 
cent, on 550 volts. 

The machine controls the arc automatically, that is if 
the carbons are put together forming a short circuit, the 



166 MOTION PICTURE ELECTRICITY 

amperes on the line will go down, as there is no power 
used for light. If the carbons are separated a great dis- 
tance up to the limit of the breaking point of the arc, the 
amperes on the line also decrease until the arc breaks. 
The following figures show the input of amperes from 
the line and the output in amperes at the arc: 



Line 


Line 


Arc 


Arc 


volts. 


amperes. 


volts. 


amperes. 


no 


15 to 20 


50 to 55 


25 to 40 


220 


8 to 12 


5o to 55 


25 to 40 


55o 


4 to 5 


50 to 55 


25 to 40 



These machines are primarily made for the purpose of 
saving on the electric bill, but they also possess the ad- 
vantage of removing the heat from the operating room, 
doing away with the rheostat entirely, and reducing the 
size of line wires, fuses, switches and other fittings, which 
in some instances become quite expensive, especially for 
amusement resorts, parks, etc., where the wires have to 
run long distances. 

Another important feature is that the machines are 
Turnished with light controllers or regulators, by means 
of which the candle-power of the projector arc lamp can 
be increased or decreased at the will of the operator. 
The controller is also intended to compensate for big 
drop in voltage on the line as often happens when the 
load is heavy on the electric company's service. 

Where the city authorities limit the amount of am- 
peres which can be taken from a line for picture projec- 
tion, these machines are very useful, because it is possible 
to get 40 to 50 amperes at the arc with only 3b ampere 
line fuses and switches, besides saving a large percentage 
on the electric bill. 

Another point of advantage is that where the electric 
company supplies current on a 3-wire system, these ma- 
chines may be connected on the two outside wires op- 
erating on 220 volts with only 10 ampere fuses, which, 
of course, prevents the usual dip in candlepower of in- 
candescent lamps on the same system every time the 
notion picture lamp is switched on. 



MOTION PICTURE ELECTRICITY 167 

CHAPTER X 

Alternating Current Projection 

DIRECT CURRENT flows in one direction continu- 
ously and is therefore sometimes called continuous 
current, and that on account of the fact that the 
direct current flows in one direction it is possible to cen- 
tralize the greater part of the heat at the positive carbon 
or crater of a direct-current arc. This centralization of 
the energy at the positive crater is very desirable for 
projector arc lamps, because it is easy to focus the light 
from one crater only. 

With direct-current arc the light rays from the neg- 
ative crater are entirely disregarded and it is not neces- 
sary or practical to bring the light rays from the negative 
crater in proper focus to assist in the illumination on the 
screen. 

The temperature at the positive crater of a direct- 
current arc is more than double the temperature of the 
negative crater, therefore the positive crater is extremely 
brilliant as compared with the negative crater. It would 
be a difficult thing to make use of the illumination from 
the crater on the negative carbon, on account of the dis- 
tance between the two carbon points or craters which 
necessarily has to be maintained in order to secure proper 
combustion of the carbons. 

It is conceded that a good average illumination can be 
secured from the positive crater of a direct-current 25- 
ampere arc and for better results the current may be in- 
creased to 30 amperes and in special instances, where a 
brilliant picture is necessary, the current at the arc may 
be increased from 30 to 50 amperes. 

In chapter 2 are described the methods of generating 
and distributing alternating current. 

With alternating current the problem is more difficult 
because of the fact that the current at the arc is inter- 



168 



MOTION PICTURE ELECTRICITY 



■*-J 1 L 




Fig. 99 



MOTION PICTURE ELECTRICITY 169 

rupted or, in other words, the arc is dead as many times 
per second as the current reverses. The number of re- 
versals of the current depends upon the cycles or fre- 
quency of the system. 

In Fig. ii you will find a graphical demonstration of 
an alternating-current system showing three complete 
cycles, and for convenience I submit the same illustration, 
Fig. 99. 

If you begin at the (o) point, you will note the cur- 
rent travels with the time up to 30 amperes in the posi- 
tive direction, that means, the upper carbon will be sub- 
ject to a positive flow of current increasing from (0) to 
30 amperes and then falling to nothing at (a), from 
which point the current continues in the negative direc- 
tion to 30 amperes, then dropping again to nothing at 
point (b) and so on. If you stop to think that between 
(o) and (b) one-sixtieth of a second has elapsed, you 
will see that the upper carbon has had one positive im- 
pulse and one negative impulse, and during the same pe- 
riod the lower carbon has received one negative and one 
positive impulse, and as it is impossible to reverse the 
current without putting the arc out, and there being two 
reversals in one cycle, the arc must have been out twice 
during one cycle. If we prolong the horizontal line of 
Fig. 99 to cover a period of one second, we would have 
just 60 cycles or 60 complete reversals on an ordinary 
60-cycle system, which makes it evident that on the 60- 
cycle system the arc is absolutely out 120 times per second. 

You should understand that for projecting work, the 
craters only are of value as a light-giving medium. The 
arc proper is of no value, it only serves as a means for 
carrying the current from one carbon point to the other 
so as to heat the carbon points to a sufficiently high tem- 
perature to volatilize the carbon, thus producing, when 
combined with the proper amount of air, the great in- 
tensity of the electric arc crater which is really the essen- 
tial element for good projection. Therefore, it is the aim 
to maintain the brilliancy and constancy of illumination 
at the carbon points as great as possible. With alternat- 
ing current this is difficult, because of the interruptions. 



170 MOTION PICTURE ELECTRICITY 

When the cycles change, the current momentarily stops, 
which gives the carbon point a chance to cool off to a 
small degree,- but at the same time to a sufficient extent 
to make it noticeable as compared with direct current 
where the temperature is practically constant. As re- 
ferred to above, the current flows first in one direction, 
then in the other, which makes the upper carbon positive 
and the lower negative at one instant and at the next in- 
stant the upper carbon is negative and the lower carbon 
is positive, and so on. The positive crater on d. c. is twice 
as hot as the negative, which means that it is, of course, 
much more brilliant. With an alternating-current arc 
the lower carbon point is just as hot as the upper carbon 
point, consequently the light-giving quality of the lower 
carbon crater is of just as great value as the crater on 
the upper carbon, which, as before stated, is not the case 
with the direct-current arc. 

With the a. c. we have an entirely different condition 
than with direct current. We must, if it is necessary to 
secure maximum illumination from the arc, be able to 
place the carbons in such a relation to each other and to 
the system of lenses on the projector machine, that not 
only the upper carbon crater can be focused, but the lower 
carbon crater as well, otherwise the illumination would 
be less than one-half as compared with direct current for 
the same number of amperes at the arc. 

The alternating current electric arc maintained ) between 
two carbon points produces different results than the di- 
rect-current arc, and the main differences may be enu- 
merated as follows : 

One : With a given number of amperes and voltage 
drop across the arc the alternating-current arc between 
two ordinary carbon points, produces about 50 per cent, 
less useful illumination for projector work than direct 
current. 

Two: The alternating current projector arc operates 
with 25 to 30 per cent, lower potential drop as compared 
with the direct-current arc. 

Three: The alternating-current arc is more unstable 
and difficult to control unless carbons of very small diam- 



MOTION PICTURE ELECTRICITY 171 

eter are used which would be impractical with projector 
lamps. 

Four: The alternating-current arc cannot be main- 
tained between one cored and one solid carbon, because 
the core of each carbon being made from a material which 
volatilizes with greater ease than the main body of the 
carbon is necessary in order to sustain an auxiliary, flame 
or medium by which the arc proper can be re-established 
after each reversal of the current. 

Five: The alternating current arc as controlled by 
rheostat cannot be maintained in proper form for projec- 
tion with the frequency below 40 cycles per second. The 
greater the number of cycles, the better and more con- 
stant will be the illumination from the carbon points of an 
alternating current arc. The tendency, however, on the 
part of the elecric lighting companies, is to install' new 
generators and transforming devices for distributing not 
to exceed 60 cycles, and most of the old systems which 
have been in operation during the past twenty years 
varying in frequency from 100 to 140 cycles have now 
been replaced ; therefore we are most concerned about the 
operation of projector arc lamps on the more modern 
systems which deliver from 25 to 60 cycles. 

Six: The alternating current arc produces craters on 
the extreme ends of the carbons of equal temperature and 
intensity. In other words, the light-giving power from 
the crater on the upper carbon is the same as on the lower 
carbon. There is, of course, a likelihood of the crater on 
the upper carbon operating at slightly higher temperature 
on account of the fact that it is generally above the crater 
on the lower carbon, which would tend to increase its 
temperature, but for practical projection purposes the 
temperature and the light-giving power of the upper and 
lower carbon craters may be considered equal. 

CARBON SETTING 

Considering what has been said previously, and the 
foregoing references to the alternating current arc, one 
can easily understand that it is absolutely necessary to 



172 MOTION PICTURE ELECTRICITY 

so arrange the carbons, the craters, and the arc, that it is 
possible to focus the illumination from both craters sim- 
ultaneously by the means of one set of lenses on one spot. 

With the ordinary methods for the setting of the arc 
lamps and carbons for motion picture projection and 
where the arc is controlled by an ordinary rheostat, a 
choke coil, or similar current-saving device, it is neither 
practical nor possible to focus the illumination from both 
craters simultaneously. 

This point is well worthy of careful consideration, and 
more thought on the subject will convince the reader that 
failures in the past when using the alternating arc for 
motion picture projection are mainly due to the neglect 
of placing the carbons in proper manner to secure illu- 
mination from both craters at the same time. 

Some motion picture operators have been satisfied with 
illumination secured from the crater on the upper carbon, 
which is the only medium available when the carbons are 
set as is customary with direct current, at an angle vary- 
ing from 20 to 25 degrees. 

It is a noteworthy fact that only 50 per cent, of the 
total illumination from both craters is used from an alter- 
nating current arc having the carbons set at an angle as 
is customary for direct current projection. 

It does not take an expert to realize that unless both 
carbon points or craters are put very close to each other 
and both craters are in exactly the same relation and po- 
sition to the condensing lenses, it is not possible to secure 
the total available illumination from an alternating cur- 
rent arc. 

Having established the fact that with the direct current 
arc carbon-setting, only the upper erater can be focused, 
it is evident without further explanation that it is abso- 
lutely necessary to use a different carbon setting than is 
customary with direct current for alternating current arc 
projection. 

I have given a great deal of thought to this subject, and 
have carefully studied and experimented with the alter- 
nating current arc for motion picture projection, and 
have come to the conclusion that an entirely different car- 



MOTION PICTURE ELECTRICITY 



173 



bon setting and method of control and operation must be 
employed with the alternating current where high effi- 
ciency, perfect illumination and regulation is to be ob- 
tained. 

The subject of the alternating current projector arc is 
very simple to those who have mastered the details, and 
unless the details have been mastered, it is impossible to 
secure universally satisfactory results with the alternating 
current arc. This statement is borne out by the fact that 




many operators who understand the details and functions 
of each element produce splendid results with alternating 
current, even with inferior current supply, carbons and 
controlling devices, whereas others produce unsatisfac- 
tory results having the best equipment possible at their 
disposal. 



174 MOTION PICTURE ELECTRICITY 

T purpose to make the matter of the alternating current 
electric arc absolutely clear to all interested in the art, 
and for that purpose I submit sketch, Fig. 100, which is a 
representation of two ^g-inch soft-cored carbons, between 
which an electric arc is maintained with alternating cur- 
rent. The illustration is intended to represent the condi- 
tion of the carbon points when the arc is operating at a 
potential drop of about 40 to 45 volts, controlled by rheo- 
stat, choke coil or the ordinary current-saving trans- 
formers. If you will analyze Fig. 100, you will find that 
the crater of the upper carbon only, is within the focus 
of the lens, due to the following reasons : 

First. — The carbons being in practically perfect align- 
ment, are tilted backwards at an angle, exposing the crater 
of the upper carbon only. 

Second. — The arc proper is practically out of focus, ex- 
cepting the upper part of it, which is in front of the upper 
crater and the presence of the arc, which cannot be 
avoided, throws a mist in front of the upper crater, which 
diminishes the illumination, and at the same time intro- 
duces the purple or violet "ghost" so common on the 
screen when the alternating current arc is used. 

Third. — The crater of the lower carbon is entirely use- 
less as an illuminating medium, because it cannot be 
brought into focus at the same time with the upper crater, 
on account of the length of the arc necessary when con- 
trolled by ordinary means, as above referred to, making 
the distance between the two carbon points too great for 
simultaneous focusing. 

Note also that the lower carbon crater faces away from 
the lenses, throwing its light in a direction opposite to 
that required. 

Considering these important points, you will agree and 
can readily make up your mind to the fact that only the 
upper carbon crater is of any value when the carbons are 
set at the angle illustrated, or, in other words, as is cus- 
tomary for direct current projection. The result of this 
condition is that only 50 per cent, of the total illumination 
available can be used with such carbon setting. 



MOTION PICTURE ELECTRICITY 



175 



One might ask the question : "Why not put the carbons 
in some other position so that both craters can be focused 
simultaneously?" This can be done to a limited extent 
with ordinary methods of arc control, as previously re- 
ferred to, but can never be done when the direct current 
setting is employed. 





Fig. 102 



For further consideration, and to make the matter still • 
more clear, I submit Fig. 101, which shows the alternating 
current arc at the instant the upper carbon receives the 
positive impulse. At that instant, the upper carbon crater 
is at maximum intensity, and the lower carbon crater is of 
much lower intensity. In fact, Fig. 101 can be compared 
with the ordinary direct current arc where the upper car- 
bon is connected to the positive wire, but only for one 
instant, or for 1/60 of a second on a 60-cycle system. 

Fig. 102 is intended to show the alternating current arc 
at the instant when the lower carbon receives a positive 
impulse, under which condition the lower crater is at 
maximum intensity, causing the upper crater to give a 
very small amount of illumination, as would be the case 



176 MOTION PICTURE ELECTRICITY 

with a direct current arc if the wires were reversed so 
that the lower carbon would be connected to the positive 
wire, which, as is generally known, would give a purple 
and unsatisfactory illumination. 

A careful consideration of Figs. 101 and 102, therefore, 
sets forth additional facts of great importance, because 
they illustrate how the alternating current are when used 
with the direct current carbon setting at an angle, not only 
has to work at the disadvantage of having only the upper 
crater subject to focusing, but at the same time, when- 
ever the frequency changes, or, in other words, when the 
current reverses, the upper carbon crater loses more than 
50 per cent, of its intensity, as compared with direct cur- 
rent. 

There is another important point which must be re- 
membered, and that is when the upper carbon on an alter- 
nating current system receives a positive impulse, it does 
not receive a full flow of current at once, or for the total 
period of the cycle, because the alternating current, when 
it flows in the positive direction, begins at zero and rises 
up to the maximum current flow, and then drops again 
to zero, which means that there is only a very short instant 
during which the full amount of current flows. 

When you compare these conditions with the direct 
current arc, the alternating current system is at a great 
disadvantage under ordinary conditions and with ordinary 
control, because with direct current, which flows continu- 
ously in one direction, the positive crater maintains con- 
tinuously maximum temperature and therefore highest 
illuminating intensity. 

Most operators are aware of these facts and overcome 
some of the disadvantages by different carbon settings, 
some of which improve the results, but the fact still re- 
mains that the alternating current projector arc operates 
at the greatest disadvantage when the carbons are set as 
illustrated in Fig. 100, or, in other words, when the regu- 
lar direct current carbon setting is used with alternating 
current. 

There are many ways for setting the carbons, and as 
we are considering the more important methods or ways 



MOTION PICTURE ELECTRICITY 177 

of setting the carbons for alternating current, a modified 
form of carbon setting for alternating current in which 
the lower carbon is placed perpendicular and the upper 
carbon is placed at an angle relative to the lower carbon, 
as illustrated in Figs. 103 and 104. 

With the ordinary means of control for the alternating 
current arc, including the rheostat, choke coils and the 
general run of current-saving transformers, there is no 
particular advantage in placing the carbons as illustrated 
in Fig. 103, because even though the lower carbon be set 
straight up and down, its crater cannot be focused simul- 
taneously with the crater of the upper carbon, due to the 
fact that the distance beween the two carbon craters is 
too great, and besides, the lower carbon faces directly up- 
wards, so that at the very most only the front upper edge 
of the lower crate would be useful as an illuminating me- 
dium, and, as already stated, it is too far below the upper 
crater to make it of any value as an illuminating medium. 

The only possible advantage with this carbon setting 
when the arc is controlled by ordinary means of current 
control, as above mentioned, lies in the fact that the lower 
carbon is swung out of the way, as you might say, of the 
upper crater, interfering less with the rays of light from 
the upper carbon crater. If you will look again at Fig. 
101, you will find that the point of the lower carbon is 
slightly in front of the lower edge of the upper carbon 
crater, cutting off some of the illumination. This trouble 
is done away with when setting the carbons as illustrated 
in Fig. 103. 

The carbon setting shown in Fig. 103 is extremely diffi- 
cult to handle, because as the upper carbon burns away, its 
crater gradually gets back further and further from the 
center of the lower carbon point, thus making it necessary 
to push the upper carbon forward or readjust the upper 
carbon clamp so that the upper carbon will be put at a 
greater angle, in that way pushing its crater forward, or 
by swinging the lower carbon point backward so as to 
maintain the same relative position, as illustrated in Fig. 
103, between the two carbon points. Expert operators 
can do these stunts, but it is a difficult job and requires a 



178 MOTION PICTURE ELECTRICITY 




MOTION PICTURE ELECTRICITY 179 

great deal of judgment and care so as not to interfere 
with the continuous operation of the light while the pic- 
ture is being exhibited. 

The gain by putting the carbons as illustrated in Fig. 
103 when the alternating current arc is controlled by the 
ordinary means, as already referred to, as compared with 
the carbon setting shown in Fig. 10 1 is not sufficiently 
great to warrant introducing the possible chance of trou- 
ble by setting the carbons as shown in Fig. 103. There- 
fore, the carbon setting as shown in Fig. 103 is not rec- 
ommended for general use with alternating current, ex- 
cepting in cases where special means of current control 
are introduced. This setting is of value, however, where 
the motion picture lamp is provided with the backward 
and forward adjustment for the upper carbon, controlled 
outside the lamp-house, as is now general in the more 
modern motion picture lamp equipment. 

To further explain the exact distribution of illumina- 
tion from the craters with the carbon setting as illus- 
trated in Fig. 103, I have introduced Fig. 104 for com- 
parison. 

Fig. 103 illustrates the arc and light distribution when 
the upper carbon receives a positive impulse, at which in- 
stant the upper crater gives maximum illumination, and 
the lower crater a comparatively small amount of illu- 
mination. Fig. 104 illustrates the reverse condition, that 
is, when the lower carbon receives a positive impulse, at 
which instant the lower crater gives the greatest amount 
of light and the upper crater a comparatively low amount 
of illumination. 

Summing up what has been said about this form of 
carbon setting, it will be easily understood by any careful 
observer that the upper carbon crater is really the only im- 
portant light-giving medium, although the upper front 
edge of the lower crater also contributes some illumina- 
tion, but a comparatively small amount. 

The foregoing arguments set forth together with illus- 



180 MOTION PICTURE ELECTRICITY 

trations and the descriptions, should clearly demonstrate 
the fact that 

with alternating current at the arc of a projector 
lamp, only one of the craters produces light of any 
magnitude at a time. 

The fact has also been brought out that on account 
of the distance between the carbon points neces- 
sary in order to maintain a proper arc with the or- 
dinary means of current control for such arcs 
prevents the focusing of upper and lower craters 
in one spot with the same system of lenses. 

Another matter of importance which has been brought 
to your attention is that 

the point or crater of the lower carbon, if said 
carbon sits straight up and down or is tilted back- 
wards, cannot be of any material benefit as an illu- 
minating medium in a projector arc, because the 
upper surface of the lower carbon being flat or 
even tilted backwards does not distribute any great 
quantity of illumination towards the condensing 
lenses, even though it should be possible to focus 
the upper and lower craters simultaneously, which 
is not practical with ordinary means of arc control, 
such as rheostats, choke coils and ordinary cur- 
rent-saving transformers. 

Those who have made a study of the alternating cur- 
rent electric arc and who have had a great deal of ex- 
perience know that the foregoing statements are abso- 
lutely correct and are borne out by practical experience. 

It would seem reasonable, in view of past experience, 
to suggest that it is possible to make use of the illumina- 
tion from both the upper and lower crater with an alter- 
nating current arc by putting the carbons at an angle 
relative to each other and to the condensing lenses, whirh 
will permit the total illumination from both craters to 
come within the reach of the condensing lenses. Such a 
carbon setting has been tried by many operators, and 
under certain conditions this carbon setting is very satis- 



MOTION PICTURE ELECTRICITY 181 

factory. Fig. 105 shows the light distribution from such 
a carbon setting when the upper carbon receives a positive 
impulse. Under these conditions, the upper carbon crater 
is at maximum intensity and within the focus of the 
lenses. 

Fig. 106 is intended to illustrate the light distribution 
with this same carbon setting at the instant when the 
lower carbon receives a positive impulse, under which 
condition the lower crater will reduce maximum illumi- 
nation and at that same instant the upper carbon crater 
produces a comparatively small amount of illumination. 

I have tried to make Figs. 105 and 106 as true to prac- 
tice as possible, and you will agree that the separation be- 
tween the two carbon points is about as small as can con- 
veniently be maintained with a proper arc with the ordi- 
nary means of current control. A study of the^ accom- 
panying illustrations should convince you that, notwith- 
standing the fact that both craters are put in a position 
where they practically face the condensing lenses, it is not 
possible to bring both craters in focus on one spot, on ac- 
count of the distance between them. The carbon setting 
illustrated in Figs. 105-106 may give more total illu- 
mination in the direction of the condensing lenses, but the 
net result is practically no better than from carbon set- 
tings illustrated in Figs. 100 and 103. 

This statement may seem unreasonable to many, but 
when the reader takes into account the point that the con- 
densing lenses of a projector arc lamp bring into focus 
on the spot at the aperture plate an exact image 
of the craters, it is easy to understand that there 
will be a very brilliant spot on the upper part of the 
aperture from the lower crater and another brilliant 
spot on the lower part of the aperture from the upper 
crater, but right in the center there will be a purple or 
violet streak which represents the arc which is not backed 
up by a crater, but which is in front of the air space be- 
tween the rear part of the upper and lower craters. 

Having mastered the foregoing argument, you will 
readily understand that in order to focus both craters in 
Figs. 105 and 106 it would be necessary to bring the rear 



182 



MOTION PICTURE ELECTRICITY 





tt/i 



MOTION PICTURE ELECTRICITY 183 

end of the carbon points together, so that they not only 
touch but overlap each other, and this is impossible to do 
and still maintain a proper arc with proper consumption 
of the carbons and proper maintenance of the shape of the 
craters using a rheostat, choke coil or ordinary current- 
saving transformer. 

Operators of experience know that if, under the condi- 
tions specified, the carbon points are put close to each 
other in the rear, that is, so close that the craters touch 
each other. In other words, if you allow the carbon 
points to freeze, the arc will be diminished, operating at a 
much lower voltage drop than normally, thereby, of 
course, reducing the number of watts at the arc. This in 
turn cuts down the candlepower of the craters, so that 
while the craters may be in that condition focused simul- 
taneously, the candlepower is so much lower that there is 
no benefit in operating under that condition. It would be 
far better to operate with only one of the craters, as illus- 
trated in Figs, ioo and 103. 

The carbon setting illustrated in Figs. 105 and 106 also 
tends to make the arc unstable, because of the very great 
distance between the front part of the craters as com- 
pared with the rear, making the illumination rather un- 
steady, as compared with carbon setting illustrated in 
Fig. 100. 

In view of the foregoing, there is no particular advan- 
tage in setting the carbons as illustrated in Figs. 105 and 
106, with ordinary means of current control. The setting 
is more complicated than the ordinary setting in Fig. 100 
and does not produce better results. There are, however, 
conditions under which it is of advantage to set the car- 
bons as illustrated in Figs. 103 and 105, but now when the 
arc is controlled by a rheostat, choke coil or ordinary 
current saving transformer. 



184 MOTION PICTURE ELECTRICITY 

CHAPTER XI 

A. C. Economizer 



OF the various carbon settings referred to, it might 
be stated that the setting illustrated in Fig. ioo 
will give universal satisfaction when the arc is 
controlled by any of the means or devices specified in the 
preceding chapter. 

It is equally true that skilled operators can produce 
good results with these devices with a carbon setting as 
illustrated in Fig. 103, although it is more difficult to ma- 
nipulate the carbons and to always keep them in proper 
relation to each other. 

It may also be taken as a fact that a carbon setting sim- 
ilar to Fig. 105 will give satisfactory results with any 
of the current controlling devices mentioned. It is, how- 
ever, generally recognized that the advantages of setting 
the carbons as illustrated in Figs. 103 and 105 are not 
sufficiently great to warrant the use of this setting as com- 
pared with the more all around satisfactory and more eas- 
ily manipulated carbon setting as illustrated in Fig. 100, 
which may be considered the standard when the arc is 
controlled by ordinary means on alternating current. 

The writer, having been in constant daily touch with the 
development of arc lamps arc lighting apparatus, arc lamp 
controllers and similar devices for many years past, has 
made an exceptionally careful study and has had unusual 
opportunities to investigate and test the electric arc under 
different conditions and for different purposes. 

Some seven years ago, I made most exhaustive tests 
and experiments with the alternating current electric arc 
for motion picture projection and established the fact that 
it is absolutely necessary, in order to secure perfect re- 
sults with a. c. at the arc, to so arrange the carbons that 
both the upper and lower craters can be focused with the 



MOTION PICTURE ELECTRICITY 185 

same system of lenses and at the same time in one single 
spot. 

These tests further demonstrated the fact that it is im- 
possible to put and maintain the carbon points close 
enough together to permit the focusing of both carbon 
craters at the same time and to eliminate the purple arc, 
with rheostat, choke coil or ordinary current saving trans- 
former control. 

As a result of the foregoing, a line of specially designed 
semi-constant current transformers were developed by 
the writer for the purpose of delivering to a projector arc 
lamp a modified current which w : ll permit the focusing 
of both carbon craters at the same time and which will 
eliminate the purple arc. These semi-constant current 
transformers are well known to the trade under the name 
of the Hallberg Automatic Electric Economizer. 

This device operates on the principle of the constant 
current transformer described in Chapter III, illustrated 
by Figs. 20 and 21. It is practically constructed along the 
lines of Fig. 21, but is provided with two or three extra 
taps in the primary winding. These taps are arranged to 
include all nine turns of the primary winding for highest 
line voltage and a lesser number of turns for medium or 
very low line voltage. For further information regard- 
ing the operation and connection of this device, study the 
chapter on the Hallberg A. C. Economizer, together with 
references to it under heading "Questions and Answers 
for Operators." 

In order to make the value and advantages of this arc 
controlling device perfectly clear to the reader, and also 
in order to demonstrate the relative advantages and dis- 
advantages of setting the carbons at the usual angle as 
illustrated in Fig. 100, as compared with the perfectly 
vertical carbon setting recommended to the users of the 
economizer, I present photographic reproductions of the 
arc phenomena and light distribution, which have been 
prepared at a considerable expense. 

The reader who has made a study of the alternating 
current electric arc will at once appreciate the extraor- 
dinary results which can be obtained by the vertical car- 



186 



MOTION PICTURE ELECTRICITY 




■W:o 

^ o C: i- 
^ ^ co U 

X>-^ o c 

no iu cv 

o 3,-o 



o 5. ' 

"^ rv v - 

■II *>.- 3 ■ 

Ex) vj 




MOTION PICTURE ELECTRICITY 187 

bon setting when the arc is properly controlled. I do not 
want the reader to get the impression, however, that the 
vertical carbon setting can be used with all kinds of cur- 
rent controllers, because it cannot. The vertical carbon 
setting was devised and recommended for use with the 
economizer only, and when used in combination with 
this device, under proper voltage and cycles, the 
best results that can possibly be obtained with a. c. at 
the arc will be realized. In fact it is possible with this 
equipment to equal a d. c. arc projection with the same 
number of watts taken from the line up to 30 ampere 
d. c. arc. 

Fig. 107 is an exact reproduction of a 45-ampere alter- 
nating-current arc maintained between two carbons set 
at the angle universally adopted for direct and alternat- 
ing current projection with ordinary means of current 
control. 

Fig. 108 is an exact representation of the same electric 
arc looking into the front of the lamp house with the 
condensing lenses removed. 

These illustrations are instructive and interesting, and 
I call your particular attention to the upper crater, which 
it will be seen is the only light-giving medium that pro- 
duces white illumination in proper focus. The purple arc 
is somewhat below and in front of the white upper crater, 
and instead of distributing illumination on the screen it 
does great harm, in that it casts a purple shadow (usually 
called the "ghost" on the screen) . Note that the purple 
arc in Fig. 108 cuts off almost fifty per cent, of the 
upper crater, reducing the candlepower. The crater of 
the lower carbon can barely be seen, as it is in its own 
shadow, and besides it is below the line of focus and is, 
therefore, of no particular illuminating value. 

Notwithstanding the fact that the arc is extremely in- 
efficient when the carbons are set as illustrated in Figs. 
107 and 108, many operators continue to use this carbon 
setting, because their current controllers do not permit 
the setting of the carbons to advantage in any other way. 

Fig. 109 is an exact reproduction of the a.- c. arc in an 



188 



MOTION PICTURE ELECTRICITY 



ordinary moving picture machine lamp house operating 
on 6o-cycle alternating current between two high grade 
y% in. soft cored carbons. The photograph from which 
this cut was made was taken after the arc had been in op- 
eration about three-quarters of an hour, so as to secure 
a reproduction of the carbon points and the arc when in 
normal use. 




Upper Garboo 
f Upper Grader 
^Short and White arc. 

in fdcuiwiCI) upper 

crater. 
^Exposed lower Crater 

m Focus witlrbotb 

upper Crater and 

Cbearc/ 

Lower Carbon. 



Fig. 109 



I desire to call particular attention to the surfaces of the 
upper and lower craters, both of which are fully exposed, 
slanting at a slight angle, opening in wedge form toward 
the condensing lenses, touching each other in the rear 
so as to form two perfectly white surfaces joining each 
other at the extreme rear point. This form of crater per- 



MOTION PICTURE ELECTRICITY 189 

mits the focusing of the upper and lower craters at the 
same time with the same system of lenses in asingle spot, 
producing practically double the amount of illumination 
as compared with the carbon setting illustrated in Fig. ioo 
and Figs. 107 and 108. 

Attention is also directed to the arc in Fig. 109. The 
arc is very short and is absolutely white, so that instead 
of being a detriment like the long purple arc referred 
to above, the arc actually increases the amount of white 
illumination and makes the crater surfaces blend together 
in a pure white light without shadows on the screen. 

In order to illustrate an absolutely perfect electric arc 
with proper carbon craters on alternating current, I show 
Fig. no, which is the ideal carbon setting for alternat- 
ing current when the arc is controlled by the economizer, 
or any other device having similar characteristics. 

Whereas, the ordinary a. c. electric arc operates at a 
voltage of anywhere from 40 to 50, the a. c. arc wUen 
controlled by the economizer, as illustrated in Fig. no, 
requires only 30 to 35 volts at the arc, which, of course, 
also means that fewer watts are required and consequently 
the saving of current is greater. 

Fig. in illustrates the Hallberg Economizer which 
controlled the arc at the time photographs for Figs. 109 
and no were taken, and just as a matter of instruction 
and advice to operators who are using this device, I 
want to say that it is of the utmost importance that the 
carbons be clamped tightly in the holders ; that the as- 
bestos covered cables be perfectly attached to substantial 
lugs ; that the lugs be securely fastened to the carbon 
clamps ; that all connections be made and maintained per- 
fectly clean and tight to secure good contact; that the 
economizer should be placed at least one foot away from 
the sheet iron lined wall, and last, but not least, that the 
line voltage does not fall below the amount specified on 
the name plate of the economizer and, of course, that the 
cycles are in accordance with the number stamped on the 
name plate. ' 



190 MOTION PICTURE ELECTRICITY 




Fig. no 



MOTION PICTURE ELECTRICITY 191 

When the above points are properly attended to, then 
the vertical carbon setting as illustrated in Fig. no will 
produce unequaled results, practically as good as can be 
had with direct current for the same number of watts 
taken from the line. 

In closing this chapter on the alternating current elec- 




Fig. in 

trie arc, I want to say that the carbon settings illustrated 
in Figs. 103 and 105 may also be used when the arc is 
controlled by the Hallberg Economizer, although there is 
no particular advantage in setting the carbons that way, 
besides it requires a more expert operator to handle the 
carbons with those settings. 



MOTION PICTURE ELECTRICITY 193 



Practical and Commercial 
Section 



194 MOTION PICTURE ELECTRICITY 

CHAPTER XII 

The Hallberg Economizer 

ALTERNATING CURRENT AUTOMATIC 
ELECTRIC TYPE 

Special Information and Instructions 



WHEN projector arc lamps are operated on alter- 
nating current it is necessary in order to reduce 
the line voltage usually supplied by the electric 
company from no to about 33 volts, which is the usual 
potential drop maintained across the arc. In the early 
days, a rheostat was used for this purpose which, instead 
of transforming the voltage, simply dissipated the differ- 
ence in voltage at the arc and the line in the shape of heat, 
at a tremendous loss of energy. 

If we consider an arc of 50 amperes at 33 volts, we re- 
quire an energy of about 1,650 watts at the arc. If we 
consider the line voltage as being no and the amperes 50, 
the input from the line approximates 5,500 watts, giving 
a loss of 3,850 watts in the rheostat. At a charge of ic 
cents per kilowatt hour, the loss in the rheostat is 38^ 
cents per hour. 

In order to reduce this great loss of current in the rhe- 
ostat, many schemes have been proposed and used, and 
among them may be mentioned the commonly known 
choke coil, also known under the name of reactive coils, 
impedence coils or inductive coils. These coils generally 
consist of one or two cores of iron around which a num- 
ber of turns of large insulated copper wire is wound. The 
effect of one of these coils upon the line is the same as 
the rheostat, but due to the fact that the current in a choke 
coil lags behind the line voltage or electro motive force, 
the magnetism created in the iron core sets up a counter 



MOTION PICTURE ELECTRICITY 195 

current which opposes the line voltage, thereby not only 
reducing the voltage, but at the same time effecting a sav- 
ing in the watts consumed. When a coil of this descrip- 
tion is used, it is connected in series with the arc, exactly 
as would be an ordinary rheostat, and if 50 amperes are 
required at the arc, there will be taken from the line 50 
amperes, consequently the line wires, fuses, switches, and 
wiring inside the building must be of a capacity of 50 
amperes, or the same as for the rheostat. There is a cer- 
tain loss in the choke coil which, while being much smaller 
than in the rheostat, is still considerable. Another mat- 
ter of importance is that whenever the rheostat, or any 
form of choke coil, is used, there is considerable flaming 
at the arc and it is difficult to centralize the illuminating 
power in a sufficiently small spot on the carbons to permit 
of proper focusing. This fact accounts for the presence 
of an uneven field of light on the screen on which there 
is present what is commonly termed a "ghost," consisting 
of a shadow in the center or at one side which may be 
either all black, or more often of purple color, seriously 
interfering with the brilliancy of the picture. 

The Hallberg A. C. Economizer is a specially designed 
transformer of the semi-constant current type, which 
means that it will take the line current at a fixed potential 
and will deliver on the secondary side a practically steady 
ampere flow, irrespective of the length of the arc. This 
economizer consists of a continuous rectangular core. On 
one core leg there is put a primary winding. On the op- 
posite core leg there is placed another coil or winding 
of larger cross section wire, to which the arc lamp is con- 
nected. The primary coil has one beginning end brought 
in through terminal No. 1. The end of the primary coil 
is, however, broken into in three separate places by ter- 
minal No. 2, which includes a certain number of turns and 
which is the one to be used when the line voltage is low. 
Terminal No. 3 includes a few more turns and is used 
when the line voltage is normal. Terminal No. 4 includes 
still a few more turns and represents the end of the pri- 
mary coil, which is used when the line voltage is high. 

Fig. in illustrates the external appearance of the 
economizer as connected to the line and to the lamp of a 



196 



MOTION PICTURE ELECTRICITY 



projection machine. The machine switch is always con- 
nected on the line side of the economizer. The asbestos 
covered cables from the lamp are connected directly to 
the lamp leads extending from the economizer. 

This type is regularly furnished for voltages ranging 
from ioo to 120 or from 200 to 220, and may be con- 
structed for 25, 33, 40, 50, 60 and 120 to 140 cycles. 



o// 

APERTURE 
PLATE 




HALLBP 



Fig 112 

On no volts, the economizer line wires are usually at- 
tached to terminals 1 and 2 for any voltage from 100 to 
105. On 1 and 3 for no volts, or to terminals 1 and 4 
if the line voltage should vary between 115 and 210. If 
the economizer is made for 220 volts, then the line wires 
are connected to 1 and 2 for 200 volts ; on 1 and 3 for 210 
volts, or to 1 and 4 for 220 volts (see diagram Fig. 112). 



MOTION PICTURE ELECTRICITY 



197 



Some operators desire varying candlepower at the arc 
to accommodate lighter, or more dense films. In a case 
of this kind, it is possible to simply install a 3-pole main 
line cut-out (with one single fuse plug) connected to the 
economizer, as illustrated in Fig. 113. By simply putting 



TO tIHE 




the plug in terminal No. 2, a heavy amperage is secured. 
Unscrew the plug and put it in. No. 3 and a medium cur- 
rent is secured, and for still less light, unscrew the plug 
and put it in terminal No. 4. This arrangement is exceed- 
ingly simple, cheap and practical and will never wear out 
or give trouble, and the plug can be instantly changed 
from one terminal to the other, giving three degrees of 
amperes at the arc. If more than one plug should be in 
the cut-out at one time the fuse will blow, because this 



198 MOTION PICTURE ELECTRICITY 

short circuits few of the primary turns on the economizer. 
Never use but one plug in the cut-out. 

"HALLBERG" ALTERNATING CURRENT 
ECONOMIZER DATA 

Lines Fuses Line Line Line Amperes 

Required Voltage Amperes Watts at Arc 

Regular Type — 30-40 Amperes 

20 no 18 1,400 30-40 

10 220 9 1,400 30-40 

Standard Type — 45-55 Amperes 

30 no 25 1,800 45-55 

15 220 13 1,800 45-55 

Special Type — 60-80 Amperes 

40 no 35 2,200 60-80 

20 220 18 2,200 60-80 

Search-Light Type — 125-150 Amperes 

80 no 75 4,200 125-150 

40 220 35 4,200 125-150 

The various Hallberg economizers, in accordance with 
the foregoing data, are intended for certain purposes, as 
follows : 

The Regular type for stereopticon work and very light 
motion picture theater work where the throw is short 
and the size of the picture is small and where the per- 
formance does not run very long at a time. 

The Standard type is the one recommended for every 
day motion picture performances. It delivers a powerful 
illumination at the arc and is good for all distances up 
to about 100 feet, and for pictures measuring as much as 
18 feet wide. 

The Special type is made for those who desire a more 
than ordinary powerful light with a. c. at the arc. It has 
been used with success for distances up to 130 feet, and 
for pictures measuring as much as 26 feet across. 

The Searchlight type economizer was originally de- 
signed for Kinemacolor work, but it proved of such great 
value as a light producer that it is now offered to the reg- 
ular motion picture trade as a means of producing the 
most perfect light which can be had with alternating cur- 
rent at the arc. It makes a brilliant white field and when 



MOTION PICTURE ELECTRICITY 199 

used with ^ inch or possibly i inch diameter carbons, it 
is entirely practical, especially when the modern large 
lamp houses are employed, such as furnished by the manu- 
facturers of all latest model machines. 

The practical operating success of the economizer de- 
pends upon a very few elements : 

1. The voltage and cycles of the current must be 
proper for the economizer. 

2. All connections, especially those between the econ- 
omizer and the carbon jaws, and also between the carbons 
and carbon jaws, must be clean and perfect. 

3. The asbestos covered cables must never be of 
smaller capacity than No. 6, and for the Special and 
Searchlight economizers, these cables should be No. 4 and 
No. 2 respectively. 

4. The proper make, style and size of carbon should 
be used as specified by the manufacturer for each type 
of economizers. 

5. The setting of the carbons should always, wherever 
possible, be in accordance with instructions furnished by 
the manufacturer. 

SPECIAL DIRECTIONS 

For the Hallberg Automatic Electric Economizer for 
Alternating Current — Standard Type 

1. Place economizer at least 12 inches away from 
sheet iron wall, as otherwise there will be a humming 
noise. 

2. 30-ampere line fuse is large enough for no, and 15- 
ampere line fuse for 220-volt circuit for standard type. 

3. Connect fuses, switches and wires exactly as illus- 
trated in Fig. 112. 

4. Make sure all connections are tight and secure, es- 
pecially at the carbon clamps in the lamp house. 

5. Cover all line terminals on economizer with tape. 

6. Use only % inch soft-cored carbons. 

7. Keep arc short, not over 1/32 inch long. 

8. Feed carbons often and very little at a time. 

9. It is better to use short carbons than to use long 



200 MOTION PICTURE ELECTRICITY 

ones, because the arc is better controlled, and the craters 
will open up toward the condensing lens, giving full il- 
lumination on the spot on the aperture plate. 

10. The carbon points and spot on the plate should 
look, as shown in Fig. 112, for best results. 

11. If, for some reason, the carbon points do not burn 
clean, as is the case if inferior carbons are used, or more 
often, if the line voltage is too low, temporarily improve 
the light by using a coarse file on the front edge of the 
upper and lower crater, which will remove the ragged car- 
bon points and expose the craters to the condensers or 
put plug in No. 2 (see Fig. 113). 

12. Low-line voltage, which sometimes happens dur- 
ing the early part of an evening when the electric com- 
pany's system is loaded heavily; inferior carbons, and 
loose connections are the three main sources of trouble. 

Operators, look out for these points and guide your- 
selves accordingly. 



HALLBERG A. C. TO D. C. ECONOMIZERS 

Special Information and Instructions 

Those who are familiar with projector arc lamps of all 
kinds understand that, as a general rule, better illumina- 
tion and more quiet operation can be obtained by the use 
of direct current applied to the arc. Alternating current, 
even under the very best conditions, makes a noisy arc, 
i*nd due to the fact that the heat is distributed equally on 
the upper and lower carbon points, it makes it difficult 
to concentrate the illumination from the upper and lower 
crater into one single spot on the aperture plate. This is 
impossible with rheostats and most forms of choke coils 
and transformers, as with these only a crater from the 
upper carbon is available as an illuminating medium, 
thus reducing the illumination with alternating current 
on the screen about 50% as compared with the same 
amount of power applied to the arc with direct current. 



MOTION PICTURE ELECTRICITY 201 

The tendency of the electric light companies through- 
out the country is now to install alternating current gen- 
erating plants and distributing systems, therefore the 
motion picture exhibitor will in a short time receive only 
alternating current from the mains of the electric light- 
ing companies. Those who have previously used direct 
current at the arc will find this change to their detriment, 
not only on account of the noise at the arc, but also on 
account of the decreased illumination and in some in- 
stances the uneven field and resultant ghost on the screen. 

To make it possible for the exhibitors, who are so in- 
clined to secure direct current at the arc from c.n alter- 
nating current supply, the Hallberg A. C. to D. C. Econ- 
omizer has been developed. It is composed of an a. c. 
motor which may be made for any voltage from ioo to 
600 volts, and for any frequency from 25 to 60 cycles, 
and it is made for either single phase, two-phase or three- 
phase current supply. 

Fig. 114 shows the external appearance of the Hall- 
berg A. C. to D. C. Economizer. On a common sub-base 
there is mounted the a. c. motor, which is directly con- 
nected to a specially wound generator. The connection 
is made by a pulley shaped insulated coupling which en- 
tirely separates the a. c. from the d. c. system, and this 
coupling can also serve as a pulley where the d. c. machine 
has to be used as a generator driven by any other motor, 
or by an engine of any kind. This is an important point 
in all Hallberg A. C. to D. C. Economizers and is con- 
sidered to be of advantage to the exhibitor, as it really 
gives him the opportunity of putting in a small engine, 
by means of which the generator can be driven in an 
emergency, if the electric power should fail, or if the out- 
fit should be installed at a point where the proper kind 
of alternating current is not available. 

The construction of the generator is along the most 
modern lines, and the arrangement of the brushes and 
connections is similar to the Hallberg D. C. Economizer, 
and the same general instructions hold good for the 
d. c. end of the a. c. to d. c. outfit. The d. c. end of this 
machine is so designed that a short circuit may be put on 



202 



MOTION PICTURE ELECTRICITY 




bo 



MOTION PICTURE ELECTRICITY 203 

it without injury to the generator — in fact, the current 
will drop down to zero if the carbons are put together 
and held that way for a few moments. This is a point of 
advantage because it protects the machine from short 
circuits or overload, and also permits the operation of 
the motion picture arc without a large rheostat in series 
with the arc. 

Wherever possible, it is desirable to operate the Hall- 
berg A. C. to D. C. Economizer on either two or three- 
phase circuits rather than single phase, and although 
made for either no or 220 volts the latter is preferable. 
The economizer is also made for single phase no or 220 
volts, but the investment is greater for the single phase 
current than for two or three-phase systems. Hallberg 
A. C. to D. C. Economizers are made in several sizes. In 
view of the fact that these machines are installed by ex- 
hibitors who appreciate the value of a picture which 
stands out in great relief where the delicate shadows in 
the half-tones and high lights are brought out to the 
greatest intensity, making the actors and scenery stand 
out life-like, which requires a powerful steady electric arc 
in the lamp house, these machines are not made up in the 
smaller sizes for general use. The following sizes are 
standardized : 

FOR ALTERNATING TO DIRECT CURRENT 







PHASE OF 


CYCLES OF DIRECT CURRENT 


TYPE 


LINE VOLTAGE 


CURRENT 


CURRENT 


DELIVERY 


A 


no or 220 v. as 


2 phase or 


60 


25 to 60 amperes 




specified 


3 phase 




with capacity for 70 
amp. for short time 
for 1 lamp, or 20 to 
30 amp. for each of 
2 lamps 


B 


no or 220 v. 
Interchangeable 


Single 
phase 


60 


Same as above 


C 


no or 220 v. as 


2 phase or 


25 


25 to 50 amperes 




specified 


3 phase 




for one lamp, or 20 
to 25 amp. for each 
of 2 lamps 


D 


no or 220 v. 


Single 


25 


Same as above 



Interchangeable phase 



204 MOTION PICTURE ELECTRICITY 

E no or 220 v. as 2 phase or 60 Up to 100 amperes 

specified 3 phase for one, two, three 

or four lamps 

F no or 220 v. Single 60 Same as above 

Interchangeable phase 

These outfits are complete, mounted on cast iron sub- 
base directly connected with light controller to increase or 
decrease the direct-current output, with complete dia- 
gram of connections and operating instructions, giving 
size of carbons required, etc. As a general rule, the elec- 
tric lighting companies permit these outfits to be operated 
without starting boxes, but in some localities, especially 
where the plant is overloaded, a starting box for the mo- 
tor end of the economizer may be insisted upon. This 
can, of course, be furnished whenever specified. These 
outfits can be made up for any other voltage or cycles, 
but those given herewith are the most common. 

The Hallberg A. C. to D. C. Economizer may be used 
for the operation of two motion picture arcs at the same 
time, as is required when it is desired to dissolve the end 
of one reel into the beginning of the other. This arrange- 
ment gives a continuous performance on the screen and 
can be accomplished by a special form of wiring and the 
installation of a double lamp control with regulating bal- 
last divided in two units, one for each lamp. This double 
lamp control arrangement can be installed at any time. 



"HALLBERG" A. C. TO D. C. ECONOMIZER 

Instructions for Operating 

1. Make sure that the machine stands on a bench or 
table elevated about 30 inches from the floor, so that the 
machine can be kept clean without the operator getting 
down on his knees. 

2. Put a good grade of dynamo or a medium automo- 
bile oil in the oil wells and make sure that when the ma- 
chine turns, the oil rings which you can see by lifting the 
cover on each oil well, rotate around the shaft, picking the 
oil from the well and properly distribute it on both sides. 
If the machine leans toward one end, the oil will run that 



MOTION PICTURE ELECTRICITY 205 

way and the other half of the bearing will not be lubri- 
cated. Drain the oil out of the well about once a month 
through the plug in the bottom and put in fresh oil. 

3. Be sure that the small springs on the brush holders 
are adjusted in the first, or weakest notch on the finger 
which presses the carbon brush against the commutator. 
If the tension is too great, the brushes will wear and the 
commutator will heat unnecessarily. 

4. When looking at the commutator on the d. c. ma- 
chine, the motor should be so connected that the commu- 
tator will operate counter clockwise or backward. 

5. The light controller or field rheostat which comes 
with the machine should be mounted at any convenient 
point in the booth. The lever should, as a general rule, 
point to the left. When the machine is first started, it 
may be necessary to move the lever a little toward the 
right. For less light, move the lever to the left side and 
for more light, move it to the right. 

6. If the economizer is to be left turning when the 
arc is not burning, for any length of time, as would be 
the case when vaudeville is mixed with pictures, then 
stop the economizer by pulling the a. c. switch, or stop 
the generator current by installing a single pole knife 
switch in series with one of the wires running from the 
economizer to the light controller. 

7. Please remember that the upper carbon should be 
24 in. cored and the lower 9/16 in. or ^g m - cored. Also 
remember if the upper carbon sits back of the lower, the 
arc is likely to climb up on front of the upper carbon and 
flare out and be very unsteady. To stop this, move the 
upper carbon slightly forward of the lower, then after 
the arc has steadied down, it can be drawn back while 
the arc is still burning, but don't let the upper crater burn 
with too much of a slant. To prevent this, move the 
upper carbon forward if it should be inclined to burn that 
way, as this will cause unsteadiness. Keep the arc 34 to 
Y% in. long. 

The wiring for the motor part of the economizer is 
standardized the same as for 5 h.p. motors, for the 25 to 
70-ampere economizer. The wiring for the d. c. «ide 



206 MOTION PICTURE ELECTRICITY 

should be of not less than No. 4 B & S gauge wire and 
the two wires which go from the field controller in the 
booth to the economizer should be No. 14 B & S gauge. 
In all cases where these machines are installed a special 
diagram of connection giving all details accompanies the 
economizer and the instructions given should be strictly 
followed. It is sometimes impossible to give exact infor- 
mation as to the position of the field controller lever, be- 
cause in some places the line voltage is high and in others 
it is low.- Then again the cycles may be below 60 or 
above 60, or may be higher or lower than the cycles for 
which the motor is made, no matter whether it be 25 or 
60 cycles. In such cases, it is necessary to set the field 
controller at the point where proper results are obtained 
and it is generally well to try out with the field controller 
in lower position, or never over the center position 
anyway. 

Many times, failure to secure steady arc is due to the 
use of too small carbons, and to the fact that the operators 
usually set the upper carbon a little back of the lower. 
With these machines, it is necessary to set the upper car- 
bon a little ahead until the arc has been struck, then the 
upper carbon may be moved back to any desired position, 
so as to give the necessary exposed crater of the upper 
carbon point, but remember that if the upper carbon is 
moved back too far, the crater will be slanting and the 
arc will be blown out on the crater, causing it to flare 
against the upper part of the condensers and to burn very 
unsteady. If the carbons are held too close together, es- 
pecially when new carbons are put in, the arc is likely to 
give a waving light, dying down and coming up again. 
The remedy is to move the arm of the field controller to 
a lower point and separate the carbons a little bit. Never 
hold the carbons too close together for any length of time, 
as this will destroy the carbon points and cause unsteady 
light. It is better to let the arc be a little longer than a 
little too short, at least until you have secured perfectly 
steady burning. In a day's operation, an operator soon 
catches on to just the best way in each instance to secure 
proper results, and this information cannot be imparted 
in detail by any instructions from the maker. 



MOTION PICTURE ELECTRICITY 



207 



For detailed instructions as to the care of the commu- 
tator, etc., see instructions given for d. c. to d. c. Hallberg 
Economizer. One thing of importance which should be 
remembered in the care of the machine is that it is always 




well to operate the brushes with the least spring tension 
which will give sparkless commutation. A stiff brush 
spring causes the brushes and commutator to wear exces- 
sively and at the same time is the cause of excessive heat 
at the commutator, due to friction. Stiff spring tension 



203 MOTION PICTURE ELECTRICITY 

does no good and is a great detriment, therefore, take 
care that the spring is in the weakest notch, which will 
give sparkless commutation, and this is generally in the 
first or weakest notch. 

The notches further back which incline to increase the 
tension of the spring should never be used unless the 
spring itself has become weakened by age. This is an- 
other point in which the judgment of the individual op- 
erator will have to be depended upon. 

Fig. 115 illustrates a specially constructed switchboard 
for use in the operating room where the current is sup- 
plied by the Hallberg A. C. to D. C. Economizer. This 
particular illustration shows the double lamp control. 
The switchboard consists of a slate slab 3 ft. high by 2 ft. 
wide, i}4 ins. thick, mounted on substantial angle iron 
frame with braces for the wall. At the top is the volt- 
meter, which indicates the voltage across the arc when one 
lamp is operating and the voltage across the generator 
when two lamps are operating. Below the voltmeter 
there are two ampere meters, one for Arc No. 1 and the 
other one for Arc No. 2. Immediately below the right 
hand ampere meter, there are three fuse connections, 
which protect the circuits. In conjunction with these 
fuses, there is a double throw switch which, when thrown 
to the left, puts the apparatus in position to operate two 
arcs at the same time. When it is desired to operate one 
arc only, this switch is thrown to the right. 

At the bottom the field controller is mounted, by means 
of which the amperage at the arc may be controlled. At 
the right of the field controller, a single pole switch is 
provided. This switch is connected in series with the 
field controller and the object of it is to disconnect the 
field circuit from the armature connection. When this 
switch is open, the generator will not produce any cur- 
rent, but will generate immediately when the switch is 
closed. 

In vaudeville houses, where pictures are run intermit- 
tently, this switch is of considerable value, or in fact in 
any theater where it is desired to give an intermission, 
because the switch may be opened, thereby saving a con- 
siderable amount on the power. 



MOTION PICTURE ELECTRICITY # 209 

THE HALLBERG ECONOMIZER 

Automatic Direct Current Type — Special Information 
and Instructions 

A projector arc lamp operating with direct current at 
the arc requires between 45 and 55 volts potential drop 
across the arc for best results. It is safe to say that the 
average voltage drop across a direct current projector arc 
is 50 volts. 

It is a well-known fact that the electric power com- 
panies do not supply current for use in theaters at a lower 
potential than 100 volts, and the average voltage is no. 
In some localities, the lowest voltage obtainable is 220 
volts, and again in a few places the only current available 
on which to operate a motion picture arc lamp is supplied 
at over 500 volts pressure. 

Taking for granted that the average arc voltage re- 
quired is 50, and that the minimum supply voltage is no, 
it is evident that there is a loss representing 60 volts, 
usually consumed by a rheostat connected in series with 
the line and the arc. 

If we consider a 30-ampere arc, this loss equals 30 
amperes times 60 volts, or 1800 watts, which is the energy 
unnecessarily wasted in heat by the rheostat on no-volt 
direct current circuit. One would think that the easy 
remedy would then be to provide a dynamo which would 
deliver 50 volts to the arc, thereby doing away with the 
losses, but unfortunately dynamos, as ordinarily con- 
structed of such small size, are inefficient and compara- 
tively expensive and besides would not operate the arc 
satisfactorily. Experience proves that about 75 volts is 
a practical voltage limit with ordinary dynamos or gen- 
erators which must then be used together with a small 
rheostat connected in series with the arc, which introduces 
more loss in addition to the losses in the generator and the 
motor necessary to drive it that no particular economy is 
effected, and it further does not pay to install an ordinary 
motor generator for the operation of projector arc lamps. 

With 220 volts supplied by the electric company, the loss 
in the rheostat is much greater, representing the difference 
between 50 and 220, or 170 volts times 30 amperes, which 



210 MOTION PICTURE ELECTRICITY 

equals over 5 kilowatts. With 550 volts the loss is tre- 
mendous, representing the difference between 50 and 550, 
which equals 500 volts times 30 amperes, or 15 kilowatts. 

With these figures before the operator, showing a loss 
on the direct current rheostat of 1.8 k.w. per hour on 
110 volts, 5.1 k.w. on a 220-volt line and 15 k.w. on a 
550-volt line, it becomes a necessity to save this great loss 
of electric energy. It is impossible to save all of it, be- 
cause the. electric arc requires a certain ballast, or steady- 
ing element, just like an engine requires a governor to 
prevent it from running away, as otherwise the arc would 
take all of the current the line wires could supply. 

In order to secure this ballast, or steadying effect, the 
rheostat has been necessary, but some four years ago the 
writer developed a line of dynamo electric machines put 
on the market under the name of the "Hallberg" Auto- 
matic Direct Current Economizers, and the purpose of 
these machines, which are made for all circuits and con- 
ditions, according to the specifications of the operator, is 
to do away with the rheostat, not only on account of the 
current saved, but at the same time removing the heat 
from the rheostat, which is uncomfortable in any operat- 
ing room, but at the same time actually improving the il- 
luminating power of the arc, because of the absence of the 
arc mist or flame, which is always present when the arc 
is operating with a considerable supply voltage back of it. 

It is true that this transformation of a high voltage into 
a lower voltage suitable for the operation of a projector 
arc cannot be accomplished without some losses, but in 
the "Hallberg" Economizer these losses have been re- 
duced to a minimum, which the following table sets forth, 
and the figures in this table are guaranteed to be practi- 
cally correct. 

"HALLBERG" DIRECT CURRENT 
ECONOMIZER DATA 









WATTS EFFI- 


LINE INPUT 


OUTPUT AT ARC 


LOSS CIENCY 


Line Line Line Line 


Arc Arc 


Arc 




fuses volts Amperes watts 


Voltage Amp. 


watts 




required 








20 A. no 17 1870 


50-55 30 


1650 


220 88% 


10 A. 220 10 2200 


50-55 30-35 


1650 


550 75% 


5 A. 550 4 2200 


50-55 30-35 


1650 


550 75% 


Note: The D. C. to D. C. 


Economizer is also 


made 


in larger sizes as 


given for A. C. to D. C. with 


one or two lamp control. 





MOTION PICTURE ELECTRICITY 



211 



The foregoing table is clear and explicit. It sets forth 
the size fuses required for. the different line voltages; 
also the number of amperes taken from the line, as well 
as the number of watts per hour required from the line to 
produce 50 to 55 volts at 30 to 35 amperes at the arc, and 
by dividing the watts produced at the arc by the input in 
watts from the line, the efficiency figures for the econo- 
mizer have been obtained. 

Fig. 123 illustrates the general make-up of the 110- 
volt type economizer which, while being constructed along 



Line fuses 

I5Am PS. Ft>f? 1 10 VbLTS 

10 - • 220 - 



Current at arc 
15 adjustable 

FROM 20 TO 




Fig. 123 



the lines of a motor generator, is in the strict sense of the 
word only in part a motor generator. The principle in- 
volved permits the use of smaller and more efficient motor 
and generator than could possibly be had if the apparatus 
was a straight motor generator set. The no-volt outfit 
is provided with an automatic starting box and light con- 
troller by means of which the operator can vary the am- 
peres at the arc anywheres from 20 to 30 on the 25-am- 
pere size; from 30 to 40 amperes on the 35-ampere size, 
and from 40 to 60 on the 50-ampere size. It is, of course, 



212 



MOTION PICTURE ELECTRICITY 







MOTION PICTURE ELECTRICITY 213 

possible to secure lower ampere output than specified as 
a minimum with any of the above machines, by the use 
of special light controllers which can be furnished upon 
request. 

Fig. 124 illustrates the "Hallberg" direct current econ- 
omizer as made for voltages ranging from 200 to 750, and 
this outfit is a straight motor generator set in which, how- 
ever, the generator is of special construction, delivering a 
steady ampere flow to the arc without the use of a rheo- 
stat. The 200 to 750-volt outfit is also furnished com- 
plete with automatic starter and light controller, and be- 
sides this outfit has a pulley coupling between the motor 
and generator on which, in special cases, a belt may be 
placed for driving the economizer by means of an engine, 
which would make the economizer operate a motion pic- 
ture arc just as it does when driven from an electric cir- 
cuit, and at the same time from the high voltage side cur- 
rent can be taken for driving fan motors, or a limited 
number of lamps. This is an important feature and is of 
considerable value to an exhibitor who might have occa- 
sion to move the economizer from one place to another. 

Another feature of this construction is that the low 
voltage side of the economizer is a separate unit which 
can be run as an ordinary dynamo by an engine ranging 
from 3 to 6 horsepower in capacity for the operation of 
a motion picture arc. The other half of the machine, rep- 
resenting the high-voltage side, is an ordinary electric 
motor which can be taken off the base in a few minutes' 
time and used as an electric motor, together with its auto- 
matic starter. These are points of economy which repre- 
sent certain advantages to the purchaser of this class of 
apparatus. 

It is not practical to give wiring diagrams showing the 
connections for these machines, because they vary for dif- 
ferent voltages and currents, and as these machines are 
generally built to specifications to suit the individual op- 
erator or manager, it is best to depend upon the blueprint 
and diagram of connections which accompany the ship- 
ment, and if the instructions should be lost, another set 
can be readily obtained at the office of the manufacturer. 



214 



MOTION PICTURE ELECTRICITY 



Fig. 125 illustrates the installation of two "Hallberg" 
direct current 40 to 50 amperes economizers operating on 
no-volt direct current, delivering 40 to 50 amperes to 
the arc of each of two moving picture lamps in one of 




Fig. 125 



Clune's Theaters at Los Angeles, Cal. The installation is 
complete, showing the switch and starting box with light 
controllers mounted back of the economizers, which are 
installed side by side on a foundation on which they did 
not have to be bolted down. 



MOTION PICTURE ELECTRICITY 215 

"HALLBERG" AUTOMATIC ELECTRIC D. C. 
ECONOMIZER 

Instructions for Setting and Operating 

Unpacking and Setting Up. — The machine should be 
unpacked carefully and installed in a dry, cool place where 
it will be free from dust and easily accessible for inspec- 
tion and care of brushes and oiling. If the operating room 
is large enough, the machine can, of course, be put there. 

Connections. — All connections should be made as 
shown on the wiring diagram sent with each machine. 
They must be clean and tight. Fuses should not have a 
higher capacity than that given on the diagram. 

Brush Tension. — After the machine has been prop- 
erly set and connected, rotate the armature by hand and 
examine each and every carbon brush, to make sure that 
it moves freely, without the slightest friction in the brush 
holder which guides it. Make sure that the flexible 
copper cable, or pigtail, as it is called, is properly clamped 
by the screw in the brush holder casting provided for that 
purpose. When the brush is in proper condition and moves 
freely in the holder, the next point to be looked after is 
the spring tension which pushes the brush against the 
commutator. This spring tension should be just enough 
to press the brush evenly but firmly against the commu- 
tator. The brush tension spring is adjustable by putting 
the end of it in the different notches provided for it in the 
brush holder casting, and any degree of tension can be 
had by using the different notches. When the brush is 
new and long, it may be proper to run it in the first or 
weakest notch. AS the brush wears away and gets 
shorter, the spring unwinds slightly and gets weaker, 
therefore it may be proper to move it in the next notch 
to increase the strength of the spring, but the judgment 
and experience of the operator will have to determine the 
brush tension required. It is sufficient to state here that 
it is always well to run with as light brush tension as pos- 



216 MOTION PICTURE ELECTRICITY 

sible to still secure sparkless operation. Dirt, overload 
and too light brush tension causes sparking. Excessive 
wear of the commutator and brushes is caused by the 
brush tension being too great. A happy medium is the 
proper thing. 

Oiling. — The oil chambers should contain enough 
oil to give the rings a good dip. The oil level will be seen 
in the gauge on the sides of the bearings and should be 
nearly at the top of the gauge. When starting the ma- 
chine, lift oil chamber covers and see that the oil rings 
are turning freely and carrying oil to the shaft. The old 
oil should be drawn of! by unscrewing the drainage plug 
at bottom of the bearing every month or two, and replaced 
with new oil. Use only light machinery or dynamo oil. 
If the oil is too heavy, the rings will not revolve and the 
bearings will not be lubricated. If the oil is too light the 
bearings will run hot. 

Setting of Brushes. — Machines are shipped from the 
factory with the brush holders and brushes properly set. 
The position of the brushes is approximately half way 
between the poles. In the motor, they are placed one or 
two segments back (that is, against the direction of rota- 
tion) of the exact middle, or neutral point, while in the 
generator they are set one or two segments forward. The 
brush holders should be placed on the studs, so that the 
brushes will not run in the same line on the commutator. 
This will help to avoid grooving. 

Starting Set. — First see that the starting box lever 
has moved back to the off position. If there is a regulat- 
ing rheostat on the motor end, its handle should be moved 
as far as possible in a counter clock-wise direction. If 
there is one on the generator end, its handle should be 
moved as far as possible in a counter clock-wise direc- 
tion. Close the main switch and move the lever of the 
starting box over the contacts, taking about one second 
for each, until it is against the magnet which will hold it. 
If the set has not started when the fourth contact point is 
reached, open the main switch and ascertain the trouble. 
When the set is running, the current may be adjusted by 
means of the regulating rheostats. 



MOTION PICTURE ELECTRICITY 217 

Stopping Set. — Open the main switch and let the 
starting box operate itself. The lever will be released 
when the motor has slowed down, when it will fly back 
to the "off" position. If the contacts become rough and 
prevent the lever from moving fully back, they should be 
cleaned with sandpaper. The lever should never be fas- 
tened or allowed to stick at an intermediate point. 

Care of Brushes and Commutator. — When starting, 
and once or twice a day, the commutator should be rubbed 
with a piece of cloth or waste having a few drops of ordi- 
nary sperm or machine oil on it. This is sufficient lubri- 
cation, and the commutator ought to assume a dark 
brown polish and run for an indefinite period with very 
little attention. Sandpaper should be used sparingly and 
only if the commutator has become rough by reason of 
sparking caused by dirt. See that the brushes are being 
held properly against the commutator by their springs, 
and that there is no friction preventing the brush from 
sliding firmly and evenly on the commutator. Make sure 
all brushes are long enough, as otherwise a short brush 
will hang up and make poor contact at the commutator, 
causing sparking, overheating and consequent injury. 



218 MOTION PICTURE ELECTRICITY 

CHAPTER XIII 

Westinghouse-Cooper Hewitt 
Rectifiers. 

The advantages of the direct-current arc lamp are 
well known. The light is steady and does not flicker. It 
is all thrown forward because the intense heat is con- 
centrated on one carbon. Focusing is a comparatively 
simple matter. 

By means of Westinghouse Type AL Cooper Hewitt 
rectifier outfit, direct-current arc lamps can be operated 
on an alternating current lighting circuit, and often more 
economically than alternating-current lamps. This is not 
strange when one considers that the direct-current arc 
requires only three-fifths as much current and that all of 
the power lost in heat in "resistance ballast" is saved by 
"reactance balance" in the rectifier. This avoids the dis- 
agreeable heat of the rheostats as well. 

The outfit consists of a Cooper Hewitt mercury rectifier 
bulb and suitable stationary regulating apparatus, all con- 
tained in a ventilated iron case. The rectifier bulb changes 
the alternating current supplied into direct current. 

The rectifier starts automatically when the lamp car- 
bons are brought together, and stops when the switch is 
opened or the carbons separated far enough to break the 
arc. 

There is no machinery to get out of order, no dirt, or 
noise. 

Standard Type AL outfits are made for no and 220- 
volt, 60-cycle, alternating-current circuits and for 30, 40 
and 50-ampere direct current. For ordinary moving pic- 
ture work a 30-ampere arc has been found sufficient, while 
for extra large screens or colored pictures 40 or 50 am- 
peres has sometimes been found desirable. 

The arc voltage is regulated between 48 and 58 volts. 
The life of the bulb, the only part that requires renewal, 
averages 500 hours or more, and an allowance is made 



MOTION PICTURE ELECTRICITY 



219 



for the return of the terminals. While outfits for 60 
cycles are standard because 60-cycle circuits are most 
common, similar outfits for other frequencies are fur- 
nished when required. On frequencies lower than 60 
cycles, such as 2^ cycles, the alternating-current flicker 
becomes so pronounced as to make a d. c. arc practically 
necessary. 



-A. C. Supply. 



S\ 



\ / 




PRINCIPLES OF OPERATION 



The mercury rectifier consists essentially of a hermeti- 
cally sealed glass bulb filled with mercury vapor and pro- 
vided with four electrodes. The two upper electrodes 
(Fig. 116) are of graphite or other suitable material and 
the two lower of mercury. The graphite electrodes are 
the anodes; the main mercury electrode is the cathode; 
and the small one is the supplementary starting electrode. 
The mercury pools of the two lower electrodes are not in 



220 MOTION PICTURE ELECTRICITY 

contact when the bulb is vertical, but the bulb is so 
mounted that it can be tilted to bring these two pools 
temporarily in contact for starting. 

The bulb contains highly attenuated vapor of mercury, 
which like other metal vapors, is an electrical conductor 
under some conditions. The anodes are surrounded by 
this vapor. Current can readily pass from either of the 
solid electrodes to the mercury vapor and from it to the 
mercury electrode, but when the direction of flow tends 
to reverse, so that the current would pass from the vapor 
to the solid electrode, there is a resistance at the surface 
of the electrode which entirely prevents the flow of cur- 
rent. The alternating-current supply circuit is connected 
to the two anodes as shown in the diagram, Fig. 116, and 
as the electrodes will allow current to flow in only one 
direction and oppose any current flow in the opposite di- 
rection, the pulsations of the current pass alternately from 
one or the other of the anodes into the mercury. As these 
currents cannot pass from the vapor into either anode, 
they are constrained to pass out all in one direction 
through the mercury electrode, from which they emerge 
as a uni-directional current. The anodes of the rectifier 
thus act as check valves, permitting current to pass into 
the mercury vapor, but preventing it from passing from 
the vapor to the solid electrodes. 

Before the bulb starts to rectify, there is a high resist- 
ance at the surface of the mercury, which must be broken 
down so that the current can pass. This surface resist- 
ance is called the cathode resistance, and it acts like an 
insulating film over the entire surface of the mercury. 
This film must be punctured, or in other words, the re- 
sistance must be overcome, before any current can pass. 
When once started, the current will continue to flow, 
meeting with practically no resistance as long as the cur- 
rent is interrupted. Any interruption of the current, 
however, even for the smallest instant of time, permits 
the cathode resistance to re-establish itself, which stops 
the operation of the bulb. 

In order to overcome this resistance the bulb is tilted 
so that the space between the main and supplementary 



MOTION PICTURE ELECTRICITY 



221 



mercury electrodes is bridged by the mercury. Current 
then passes between the two mercury electrodes from the 
source of e. m. f., and the little stream of mercury- which 
bridges the space between the electrodes breaks with a 
spark as the bulb is returned to a vertical position. This 
spark breaks down the negative electrode resistance, after 
which the rectifier will continue to operate indefinitely as 
long as the current supply is uninterrupted and the direct- 




Fig. 117 

Diagram Showing Current Waves and Impressed Electromotive 
Fo rce 



current load does not fall below the minimum required 
for the arc. 

The action of the rectifier will be better understood by 
reference to the accompanying diagram, Fig. 117, of cur- 
rent waves and impressed electro-motive force. It should 
be emphasized that the whole of the alternating-current 
waves on both sides of the zero line is used. The two 
upper curves in the diagram show the current waves in 
each of the two anodes, and the resultant curve III rep- 
resents the rectified current flowing from the cathodes, 



222 



MOTION PICTURE ELECTRICITY 



Curve IV shows the impressed alternating current e. m. f . 
It is evident that if the part of the wave below the zero 
line were reversed, the resulting current would be a pul- 
sating direct current with each pulsation varying from 
zero to a positive maximum. Such a current could not be 
maintained by the rectifier, because as soon as the zero 
value was reached the negative electrode resistance of the 
rectifier would be re-established and the circuit would 
be broken. To avoid this condition, reactance is intro- 
duced into the circuit, which causes an elongation of cur- 
rent waves so that they overlap before reaching the zero 



Rectifier 



, ooflooMooooooo ■> 1 oooooooAoo ■'■ feo r— 



Auto - Transformer 




Fig. 1 18 



value. The overlapping of the rectified current waves 
reduces the amplitude of the pulsations and produces a 
comparatively smooth direct current as shown in curve III. 
The complete circuit of a type Ai rectifier outfit is 
shown in Figs. 118 and 119. The alternating current 
supply circuit is connected at A and C, which run to taps 
2 and 5 on an auto-transformer whose terminals 1 and 7 
are connected to the anode terminals of a rectifier bulb. 
From the lower cathode terminal of the bulb the current 
passes through lead C to the lamp which is connected to 
D and C, and the circuit is completed through the lead D, 



MOTION PICTURE ELECTRICITY 



223 



and the relay to the middle point of the auto transformer. 
Bringing the lamp carbons together closes the follow- 
ing circuit : A. C. terminal C to tap 5, through auto trans- 
former to tap 4, through lead D to lamp, through lamp 
to terminal C, through contacts of relay to tilting magnet, 
through tilting magnet to tap on lead A. This excites the 
tilting magnet and tilts the bulb so the two mercury pools 
unite. At the same time the alternating current in the 
tilting magnet induces a voltage in the small starting 
winding wound with it, which causes current to flow be- 




Fig. 119 



tween the mercury pools as soon as they unite. This cur- 
rent acts like a short-circuit on the tilting magnet, and 
the bulb rights itself, causing a spark which breaks down 
the cathode resistance and starts current through the bulb 
from the main anodes. This current flows through the 
relay coil and opens its contacts which opens the tilting 
magnet circuit. 

Figs. 120 and 121 show diagrams of connections of 
the 50-ampere outfits, the operations of which are sim- 
ilar to those of the 30-ampere. 



224 



MOTION PICTURE ELECTRICITY 



PffiGRAM Of COA/MeCTtoNS- 




Fig. 120 



0MG#%A4 Of 



coH/tdzcr/o/ts 




Fig. 121 



INSTRUCTIONS FOR INSTALLING AND 
OPERATING 

To Connect Rectifier. — Connect the rectifier termi- 
nals marked A and C to an alternating-current supply 
circuit of the voltage and frequency stamped on the recti- 
fier name-plate. The outfit should be connected through a 
switch and fuses of proper capacity, as follows : 



MOTION PICTURE ELECTRICITY 225 

AL RECTIFIERS 







Line Fuse 






Capacity 


/olts. 


D. C. Amperes. 


Amperes. 


no 


30 


70 


220 


30 


40 


no 


40 


no 


220 


40 


65 


no 


50 


150 


220 


5o 


85 



Connect leads marked D — and Cf to the lamp circuit, 
taking account of proper polarity. Place bulb carefully in 
holder, and attach spring clips as per diagram. 

To Start Arc, close carbons together until a bright 
glow shines between them and then pull apart until the 
desired light is obtained. Never hold the carbons to- 
gether longer than necessary, as it may injure the bulb. 

To Extinguish Arc, pull carbons apart until arc 
breaks, or open line switch. 

For various primary voltages connect leads to binding 
posts as per following table. The primary voltage here 
referred to is that existing while the oufit is in operation 
and not that on open circuit. 

For no or 225 volts, primary, connect 3 and 5 
" no or 220 " 3 and 6 

" 108 or 215 " " " 2 and 5 

" 105 or 210 " " " 2 and 6 



226 MOTION PICTURE ELECTRICITY 

CHAPTER XIV 

Isolated Electric Lighting 
Plants 



A WORK of this kind would be incomplete without 
some reference to individual or isolated electric 
generating plants. 

It goes without saying that direct current with good 
regulation, at the proper voltage, and at a reasonable 
price, is the ideal current, but it is equally true that the con- 
ditions covered by the above apparently simple require- 
ments are almost never met with. 

Alternating current is not so well suited for moving pic- 
ture work, and under many conditions is almost 
intolerable. 

In A. C. the direction of flow is constantly reversing, 
the arc being actually extinguished and re-formed twice 
during each complete alternation. This allows the car- 
bon points to partially cool, the result being that it is im- 
possible to secure as large a volume of light from A. C. 
as from D. C. current, using the same amount of energy. 

In general, it may be stated, roughly, that from 40 to 
50 per cent, more current is required with A. C. than with 
D. C. This means that where in a given instance 30 am- 
peres of D. C. would suffice, it might take 45 to 50 am- 
peres of A. C. 

Each period of alternation is known as a cycle, and the 
number of cycles per second denotes the frequency of 
current. If of low frequency (60 cycles may be consid- 
ered as being low) the light is very unsteady, under many 
conditions almost intolerable, and the situation is, of 
course, aggravated by poor regulation. An arc operated 
with A. C. is always more or less noisy ; the higher the 
frequency, the noisier. 



MOTION PICTURE ELECTRICITY 227 

In many places where alternating current only may be 
obtained, many of the larger show-houses use A. C. to 
D. C. sets to secure direct current. While the apparatus 
itself is somewhat expensive, this expense is often war- 
ranted by the saving of current and the obtaining of a 
superior light. 

Now, as to regulation. In very many small towns and 
villages the lighting service is an adjunct to a grist mill, 
planing mill, or some sort of factory, and the producing 
of current for sale is a secondary consideration, a sort 
of by-product as it were. The power plants owned by 
such concerns are rarely ever designed for lighting, and 
the result is that there is no regulation whatever. Some- 
times there is no evening or night current furnished, ex- 
cepting specially and at an excessive cost. 

Where, on the other hand, as is often the case, the plant 
is owned by the municipality or village, and used only for 
street and house lighting, the show owner is unable to 
get current in the daytime, and this may cut into his pos- 
sible revenue to the extent of twenty-five to thirty-five 
per cent. 

Continuing the matter of regulation, it is true that in 
the majority of small cities and towns the central station 
equipment is apt to be archaic, inferior, or poorly looked 
after. From a recent number of the "Electrical World" 
I quote: 

"We have occasionally remarked on the very poor volt- 
age regulation which commonly exists among isolated 
plants. Probably a thorough investigation among small 
central station companies would reveal the condition as 
almost deplorable. Lamp salesmen who have made it a 
point to investigate regularly tell some surprising stories 
as to the lack of regulation. Frequently it has been found 
that plants giving service nominally at no volts are found 
to be actually delivering all the way from 90 to 130 volts/' 
We may now consider the matter of voltage. The actual 
voltage required at the arc is from, say 40 to 55 volts, 
variations being caused by the amperage of the arc as 
well as by the quality and density of the carbons used, 



228 MOTION PICTURE ELECTRICITY 

and there must be in series with the arc suitable resistance 
or ballast to maintain a constant, quiet arc. The arc- 
resistance decreases with increased temperature, so that 
without a suitable ballast the amperage would increase in- 
definitely on a constant potential circuit. Therefore, 
there must be an allowance of not less than twenty-five 
per cent, of the arc voltage to be absorbed by the resist- 
ance. Thus it will be understood that a current of 60 
volts may be sufficient, and 70 volts ample, for almost 
any condition. 

Current as ordinarily obtained from lighting companies 
varies, being rarely less than no volts, and from that up 
to 220. From what is stated above, it will therefore be 
understood that all current above 50 volts is absorbed 
and wasted in the rheostat, so that when one is paying for 
220-volt current the loss is very great. 

As a not altogether unusual example. I may cite an in- 
stance which recently came under my notice, of a theater 
owner who had been obtaining current from a local com- 
pany whose output was 220 volts alternating current. 
The arc was controlled by a rheostat and consumed slight- 
ly over 50 amperes. This was charged for at the rate of 
8 cents per k.w. unit. The consumption of 50 amp. at 
220 v. is 11 k.w., which at the perhaps not excessive price 
of 8 cents made the running cost 88 cents per hour. After 
some study and investigation, a small gas engine driven 
plant with 65-volt generator was purchased and installed, 
with most gratifying results. While the cost of current 
was reduced from 8 to less than 4^ cents per k.w., this 
was, however, by far the least of the saving. With direct 
current the consumption at the arc went down to 33 am- 
peres, which at 65 volts made a consumption of but little 
over 2 k.w., or a cost per hour of less than 10 cents as 
compared with 88. 

Taking up the subject of price, this is a most serious 
question. The cost of electric current is an important 
item of expense in a picture theater. It is not at all 
unusual to find instances in which theaters using from 
1,000 to 2,000 k.w. per month are being charged at the 
rate of 8 or 9, or even up to 15 cents per unit. The thea- 



MOTION PICTURE ELECTRICITY 229 

ter owner may reduce this expense by owning his own 
electric generating plant. 

As a matter of fact, there are hundreds of privately- 
owned small plants in use at the present time, and the 
chief aim of this article is to be somewhat helpful to the 
reader whose opportunities for gaining an intimate knowl- 
edge of the subject are limited. 

While it is not within the province of a writer of a 
work of this kind to recommend any one particular make 
of plant, or to criticize and condemn any other particular 
make, he is well within his rights in setting forth certain 
conclusions which are the result of many years' experi- 
ence with internal combustion engines and electrical ap- 
paratus. 

The first thing to be considered is the gas or gasoline 
engine, and it may be well to say right here that the type 
of engine in common use is entirely unsuitable for mak- 
ing electric light. Nine-tenths of all the engines sold for 
many years have been— and are — of the "Hit-or-miss" or 
constant charge type. 

When running at full power such an engine takes a full 
charge every cycle (four strokes). When running at 
half power it will take a charge and miss the next, or two 
charges and miss the next two or three, and so on. The 
result is that the speed varies, speeding up after charges 
and slowing down before, the rate of speed varying from 
as little as 5 to as much as 20 per cent. This variation in 
speed is not serious where such an engine is used for 
farm or factory purposes, but is quite "impossible" when 
electric light is to be made. Many makers of such en- 
gines equip them with extra heavy flywheels, which rem- 
edy the trouble somewhat, and, while this may — and does 
— sometimes prove fairly satisfactory, it is only in the case 
of large engines with very heavy flywheels. I have 
never seen an engine of this type under 50 horsepower 
that even with the heaviest flywheels gave really satis- 
factory results. 

The reason for the existence of this type of engine is 
that it is cheap and easy to build. Having a mixing valve 
in place of carburetor, there are no carburetion difficul- 



230 MOTION PICTURE ELECTRICITY 

ties to overcome, and, as stated previously, for ordinary 
power work, close regulation and evenness of speed is not 
a requisite. In projection work, however, the moment an 
engine runs below speed, the lights dim. If much above 
speed, the lamps are burned out, or the life is shortened. 
The speed of the engine changing constantly makes a 
variable light, which is most unsatisfactory and annoying. 

The only type of engine suitable for electric work is 
what is known as the graduated charge or "throttling" 
type. In this engine there is no hit-or-miss effect, the en- 
gine taking a charge for every cycle of operation, and the 
charge being automatically graduated to the load. While, 
as stated above, this is the only type of engine suitable 
for electric work, all so-called throttling engines are not 
capable of making a good light, as many manufacturers 
of rather indifferent hit-or-miss engines have a habit of 
substituting an inefficient governor mechanism and mix- 
ing valve, and recommending them for electric light work. 
As a matter of fact, there are too many novices in the gas 
engine business, and so far as actual knowledge is con- 
cerned, a man may have been in the gas engine manufac- 
turing business for twenty years and still remain a novice. 

As stated elsewhere, it is not my province to recom- 
mend any one particular make of plant, but I am justified 
in naming here a few old, reliable, well-established con- 
cerns which have made a specialty of electric lighting 
plants. This information is gratuitous, and the list covers 
the only firms I know of at the present time, viz. : 

Brush (C. A. Strelinger Co., Detroit), 
Nash (National Meter Co., New York), 
Westinghouse (Westinghouse Machine Co., Pitts- 
burgh), 

General Electric Co. (Schenectady), 
Otto (Philadelphia). 

All of the above concerns make direct-connected out- 
fits, and a few words here about the advantages of di- 
rect connection may not be out of place. 

First of all, the outfit is much more compact, and sel- 
dom takes up more than one-quarter of the room of a 



MOTION PICTURE ELECTRICITY 231 

belted outfit. Furthermore, there being no belt strain and 
friction on the bearings of both engine and dynamo, it 
may be depended upon to give from 10 to 15 per cent, 
more power. Naturally, a direct-connected outfit is lon- 
ger-lived, saving as it does much friction wear on both 
engine and generator shaft and bearings. It is necessar- 
ily a higher-priced form of construction. First, on ac- 
count of the sub base and expense of connecting; second, 
on account of using a much slower speed, and consequent- 
ly higher-priced generator. However, this difference is 
overcome to a considerable extent by the absence of cost 
of belts and their care, extra cost of foundation, and much 
longer life of the outfit. A final distinct advantage of the 
direct-connected plant lies in the fact that the outfit is 
set up and tested as a whole, and goes to the purchaser as 
a complete unit, whereas in belted outfits they are usually 
considered separately, and not once in a dozen cases are 
they ever tested together. Anyone who has had much to 
do with either gas engines or electric generators knows 
that such machines have their own little characteristics, 
and when one is adapted and fitted to the other, after 
thorough testing out, the results are invariably superior. 
Having had many inquiries and questions about two- 
cycle engines, I feel that some readers might like to have 
a little information in regard to this type. As Mr. 
George Fitch, the noted humorist, writes : "Nobody can 
ever hope to learn the true inwardness of the two-cycle 
engine." I know that they are sold in large numbers for 
use in boats ; that the exhaust has a pervading odor of 
unburnt gases ; that the fuel consumption is said to be 
from 50 to 100 per cent, greater than that of a four-cycle 
engine ; and, finally, that starting out with flying colors in 
the automobile field some eight or ten years ago, they 
have died an inglorious death— in that line. 

The manufacturing of electric generators in this coun- 
try is in the hands of perhaps not more than forty con- 
cerns. Ten of these produce perhaps no less than ninety 
per cent, of the electric generators and motors sold in this 
country, and of these ten concerns it may truthfully be 
said that the product of any — or all — of them is excellent. 



:32 



MOTION PICTURE ELECTRICITY 



In the manufacture of gas engines the conditions are 
quite different. There are no less than two hundred and 
fifty concerns engaged. Not more than ten per cent, of 
these concerns turn out a strictly first-class product, and, 
unfortunately — for the user — the product of some of the 
largest and most advertised is the least desirable as far 
as quality is concerned. 

In closing this chapter, I might suggest that the pur- 
chaser of an electric lighting plant will do well to con- 




Fig. 122 



sider carefully and take into account the quality of equip- 
ment and accessories that the manufacturer includes. I 
refer to the switchboard and instruments, the ignition sys- 
tem, such as batteries and coils — or magneto, if that be 
the system — tanks, tools, and so forth. 



MOTION PICTURE ELECTRICITY 233 

Fig. 122 illustrates the Brush Electric Lighting Set, 
which is one of those recommended as thoroughly reliable 
and of high efficiency and guaranteed to give service. 
The illustration shows the engine directly connected to 
electric generator of the highest quality, and there is fur- 
nished with this outfit a switchboard containing the nec- 
essary controlling switches, field regulator and Weston 
volt and ampere meter, all complete. 

The plant illustrated is about 5 k.w. capacity. There is 
also a smaller outfit made with single-cylinder engine of 
smaller type which delivers only 2 k.w., and is of just the 
right size for traveling shows. This type of engine may 
also be had in larger capacity when both motion picture 
arcs and incandescent lights are to be operated at the same 
time. The cost of these plans is necessarily higher than 
would be the cost of inferior make engines and generators 
with a fewer number of accessories, or with accessories 
of poorer quality, but the extra charge for this equipment 
will more than pay for itself in a very short time. An out- 
fit of this sort is of no use whatever to an exhibitor, un- 
less it first of all is thoroughly reliable, so that in making 
your selection, don't let price influence you. If you do, 
you will come to sorrow in the long run, and I could point 
to hundreds of plants where cheap engines and dynamos 
with inferior fittings have been installed, which have be- 
come worthless in six months 01 a year's time. 



MOTION PICTURE ELECTRICITY 235 



Practical Suggestions 



236 MOTION PICTURE ELECTRICITY 

Data and Tables for 
Projection 

TO FIND THE POSITIVE CRATER OF A 
D. C. ARC 

Whenever using direct current, it is necessary that the 
positive wire be connected to whichever carbon is to main- 
tain the positive crater, and in ordinary projector lamps 
the upper carbon should be positive. Connect the wires, 
strike the arc, let it burn from 10 to 20 seconds, pull the 
switch, and if the upper carbon is hotter than the lower 
your line wires are properly connected ; if not, reverse the 
connections at the arc lamp. 

With flaming arc lamps on direct current, proceed in a 
similar manner, and make sure that the larger carbon is 
the positive or the reddest after the test from 10 to 20 
seconds. If the arc is maintained longer than this period, 
the carbon points are both too hot to decide which shows 
the most heat, hence the advice for a short period of test. 
With alternating current there is, of course, no necessity 
for connecting the lead wires in any particular ma mer, 
as the current reverses and there is no definite positive 
pole. 

MACHINE SWITCHES 

In addition to the regular switch on the machine, each 
stereopticon, spot-light or moving-picture machine should 
be protected by an approved double-pole switch, equipped 
with fuses of approved type, keeping in mind that the 
fuses and the switch should be so connected that the 
fuses are always on the line side of the switch. It is 
readily understood that, if the fuses are on the machine 
side, an accidental short-circuit of the switch-blades would 
blow the main fuses in some other part of the building, 
causing serious delay and inconvenience. 



MOTION PICTURE ELECTRICITY 237 

CONNECTING MOVING PICTURE MACHINES 

AND STEREOPTICONS FOR TRAVELING 

EXHIBIT 

Never attempt to make connections for the above class 
of apparatus until you have carefully investigated the sup- 
ply wires, transformers, meters, fuses and switches and 
other accessories, to ascertain if they are of sufficient 
capacity to stand the increased load which will be applied 
through the connecting of such lamps. If you are in 
doubt, don't "copper" fuses. 

Don't put a jumper around the meter or connect ahead 
of the meter. 

Avoid risk and possible trouble and expense by consult- 
ing the superintendent of the electric lighting company, 
or, if supplied by a private plant, consult the electrician or 
engineer in charge. You cannot afford to jeopardize the 
success and safety of your performance by using make- 
shift methods. 

SIZE OF WIRE FOR STEREOPTICON, SPOT- 
LIGHT AND MOTION PICTURE MACHINES 



The Board of Fire Underwriters issue rules which can 
be had for the asking, setting forth the proper size and 
kind of fuses, switches, wires and cables which may be 
safely used for stereopticon, spotlight and motion-picture 
machine lamps, but for the convenience of those who do 
not know the rules, I will make the brief statement that 
No. 6 B. & S. wire or cable is the smallest which is offi- 
cially approved for a circuit supplying one such lamp re- 
quiring from 25 to 45 amperes from the line. Where the 
Hallberg Economizer or a similar device is used, the cir- 
cuit wires may be smaller when properly protected by 
fuses, but between the economizer and the arc lamp, asbes- 
tos-covered copper cable of at least No. 6 B. & S. gauge 
must be used. See also page 239. 



238 MOTION PICTURE ELECTRICITY 

CURRENT REQUIRED FOR MOTION PICTURE 
PROJECTION 

Where direct current is supplied, 25 amperes is about 
the minimum amount of current which can be used for 
ordinary projection. Where the distance from lens to 
screen is comparatively great, or where a large picture is 
required, or in cases where an extra brilliant picture must 
be shown, from 30 to 60 amperes is necessary. 

With alternating current supply, for ordinary projec- 
tion, 40 amperes is about the minimum, and as a general 
rule 45 to 50 amperes is required for good results. In 
special cases where the projection is comparatively long, 
or picture is large, or extra brilliancy is desired, as much 
as 70 amperes may be required. 

CURRENT REQUIRED FOR STEREOPTICON 
PROJECTION 

With direct current, 10 to 15 amperes gives sufficient 
illumination for ordinary stereopticon work, but for pro- 
fessional, high-class exhibit as much as 25 amperes may 
be required for large pictures and long distances. With 
alternating-current supply, 15 amperes is the minimum, 
and for best results as much as 35 amperes is required. 

REDUCTION IN SIZES OF LINE WIRE, FUSES 

AND SWITCHES WITH THE HALLBERG 

ECONOMIZER 

When the "Hallberg" is installed, the maximum am- 
peres required on 1 10 volts direct current is 25, and with 
alternating current, 30 amperes. With 220 volts direct 
current, 12 amperes, and with alternating current, 15 
amperes. With 50x3 volts direct current, 6 amperes, and 
with alternating current, 7 amperes. 

It is, of course, understood that where the "Hallberg" 
or similar device is not installed, this reduction in the size 
of line wires, fuses and switches is not permissible, as 
they must be of the full ampere capacity required by the 
arc under maximum conditions. 



MOTION PICTURE ELECTRICITY 239 

ALLOWABLE CARRYING CAPACITY OF 
COPPER WIRES 

(Fire Underwriters' Rule) 





TABLE A 


TABLE B 






RUBBER 


OTHER 






INSULATION 


INSULATION 




B & S. G. 


AMPERES 


AMPERES 


CIRCULAR MILS 


18 


3 


5 


1,624 


16 


6 


10 


2,583 


14 


15 


20 


4,107 


12 


20 


25 


6,530 


10 


25 


30 


10,380 


8 


35 


50 


l6,5IO 


6 


50 


70 


26,250 


5 


55 


80 


33,I0O 


4 


70 


90 


41,740 


3 


80 


IOO 


52,630 


2 


go 


125 


66,370 


1 


100 


150 


83,690 





125 


200 


105,500 


00 


150 


225 


133,100 


000 


175 


275 


167,800 


0,000 


225 


325 


2II,600 


CIRCULAR MILS 








200,000 


200 


300 




300,000 


275 


400 




400,000 


325 


500 




500,000 


400 


600 




600,000 


450 


680 




700,000 


500 


760 




800,000 


550 


84O 




000,000 


600 


920 




1,000,000 


650 


I,O00 




1,100,000 


690 


1,080 




1,200,000 


730 


1,150 




1,300,000 


770 


1,220 




1,400,000 


810 


I,2O0 




1,500,000 


850 


1,360 




1,600,000 


890 


1,430 




1,700,000 


930 


1,490 




I,800,000 


970 


1,550 




1,000,000 


1,010 


I,6lO 




2.O00.0OO 


1,050 


1,670 





240 



MOTION PICTURE ELECTRICITY 



The lower limit is specified for rubber-covered wires 
to prevent gradual deterioration of the high insulations 
by the heat of the wires, but not from fear of igniting 
the insulation. The question of drop is not taken into 
consideration in the above table. 

The carrying capacity of Nos. 16 and 18 B. & S. gauge 
wire is given, but no smaller than No. 14 is to be used, 
except as allowed under rules for fixture wiring. 

DIAMETER, WEIGHTS AND RESISTANCE OF 
COPPER WIRE 







Weight, 


Weight, 












Bare Wire '. 


Bare Wire 


Resistance at 75° Fahrenheit 


No. 


Diam- 


Area Pounds 


Pounds 








B. & 


eter 


Circular 


per 


per 
Mile 1 


Ohms per 
[,ooo Feet 


Ohms 


Feet per 


S. 


Mils 


Mils 


1,000 


per Mile 


Ohm 








Feet 










0000 


460.000 . 


211600.0 


640.73 , 


3383.04 


.04904 


.25891 


20939.2 


000 


409.640 


167805.0 


508.12 


2682.85 


.06184 


.32649 


16172.1 


00 


364.800 


133079-0 


402.97 


2127.66 


.07797 


.41168 


12825.4 





324-950 


105592.5 


319-74 


1688.20 


.09827 


.51885 


10176.4 


1 


289.300 


83694-5 


253-43 


1338.10 


.12398 


.65460 


8066.0 


2 


257.630 


66373.2 


200.98 


1061.17 


.15633 


.82543 


6396.7 


3 


229.420 


52633.5 


I59-38 


841.50 


.19714 


1.04090 


5072.5 


4 


204.310 


41742.6 


126.40 


667.38 


.24858 


1. 31248 


4022.9 


5 


181.940 


33102.2 


100.23 


529-23 


•31346 


1.65507 


3190.2 


6 


162.020 


26250.5 


79-49 


419.69 


.39528 


2.08706 


2529.9 


7 


144.280 


20816.7 


63.03 


332.82 


•49845 


2.63184 


2006.2 


8 


128.490 


16509.7 


49-99 


263.96 


.62849 


3.31843 


1591-1 


9 


H4-430 


13094.2 


39.65 


209.35 


.79242 


4.18400 


1262.00 


10 


101.890 


10381.6 


31-44 


165.98 


.99948 


5.27726 


1000.50 


11 


90.742 


8234.11 


24-93 


131.65 


1.26020 


6.65357 


793-56 


12 


80.808 


6529.94 


19.77 


104.40 


1.5890 


8.39001 


629.32 


13 


71.961 


5178.39 


15-68 


82.792 


2.0037 


10.57980 


499.06 


14 


64.084 


4106.76 


12.44 


65.658 


2.5266 


13.34050 


395-79 


IS 


57-o68 


3256.76 
2582.67 


9.86 


52.069 


3.1860 


16.8223 


313.87 


16 


50.820 


7.82 


41.292 


4.0176 


21.2130 


248.90 


l l 


45-257 


2048.20 


6.20 


32.746 


5.0660 


26.7485 


197-39 


18 


40.303 


1624.33 


4.92 


25.970 


6.3880 


33-7285 


156.54 


19 


35.890 


1288.09 


3-90 


20.594 


8.0555 


42.5329 


124.14 


20 


31-961 


1021.44 


3.09 


16.331 


10.1584 


53.6362 


98.44 


21 


28.462 


810.09 


2-45 


12.952 


12.8088 


67.6302 


78.07 


22 


25-347 


642.47 


1-95 


10.272 


16.1504 


85.2743 


61.92 


23 


22.571 


509-45 


1.54 


8.145 


20.3674 


107.540 


49.10 


24 


20.100 


404.01 


1.22 


6-4593 


25.6830 


135.606 


38.94 


25 


17.900 


320.41 


•97 


5.1227 


32.3833 


170.984 


30.88 


26 


15.940 


254.08 


• 77 


4.0623 


40.8377 


215.623 


24.49 


27 


14-195 


201.50 


.61 


3.2215 


51-4952 


271.895 


19.42 


28 


12.641 


159.80 


.48 


2.5548 


64.9344 


342.854 


15.40 • 


29 


11.257 


126.72 


.38 


2.0260 


81.8827 


432.341 


12.21 


30 


10.025 


100.50 


.30 


1.6068 


103.245 


545.133 


9.686 


3'i 


8.928 


79.71 


.24 


1.2744 


130.176 


687.327 


7.682 


32 


7-950 


63.20 


.19 


1. 0105 


164.174 


866.837 


6.091 


33 


7.080 


50.13 


-15 


.8014 


207.000 


1092.96 


4.831 


34 


6.304 


39-74 


.12 


•6354 


261.099 


1378.60 


3.830 


35 


5.614 


3i-52 


.10 


•5039 


329.225 


1738.31 


3-037 


36 


5.000 


25.00 


.08 


•3997 


415.047 


2191.45 


2.409 


37 


4-453 


19.83 


.06 


.3170 


523.278 


2762.91 


1,911 


38 


3-965 


15.72 


•05 


•2513 


660.011 


3484.86 


I.5I5 


39 


3-531 


12.47 


.04 


•1993 


832.228 


4394-16 


1.2020 


40 


3-144 


9.88 


.03 


.1580 


1049.718 


5542.51 


.9526 



MOTION PICTURE ELECTRICITY 241 



FIGURING PROPER SIZE OF WIRE 

For figuring proper size of wire for any given number 
of amperes and distances of a building, the rule is : 

Cx D x2i 
= Circular Mils 



Loss 

In this formula, C equals current in amperes, D equals 
distance in feet between the source of supply and the load. 

Explanation : Suppose we have a moving picture arc 
requiring 40 amperes and the distance between the source 
of supply and the moving picture machine is 30 feet ; also 
taking for granted that the loss figures at 1% for this 
class of wiring within buildings, then the formula will be 
made up as follows : 

40 x 30 x 2 1 

= Area in 25,200 circular mils. 



If we will refer to the above table, we will find that the 
nearest size wire would be No. 6 B & S, which measures 
26,250.5 circular mils, and this will be the correct size 
wire to use. 

The foregoing formula can be used for any capacity 
and for any distance, and by its use in conjunction with 
the foregoing tables, giving the gauge of wire and its 
corresponding area in circular mils, it is very easy to fig- 
ure the size wire required. 



242 



MOTION PICTURE ELECTRICITY 



TABLE SHOWING THE DIFFERENCE 
BETWEEN WIRE GAUGES 





AMERICAN 




BIR- 


W. & M. 








OR 


OLD ENG- 


MING- 


AND 


NEW 






BROWN & 


LISH OR 


HAM OR 


ROEB- 


BRITISH 


U.S. 


NO. 


SHARPENS 


LONDON 


STUBS 


LING STANDARD 


STANDARD 


oooo 


.460 


•454 


•454 


•393 


400 


.406 


ooo 


.40964 


.425 


.425 


.362 


•372 


•375 


oo 


.36480 


.380 


.380 


•331 


.348 


•344 


o 


.32495 


•340 


.340 


•307 


.324 


.313 


I 


.2893O 


.300 


.300 


.283 


.300 


.281 


2 


.25763 


.284 


.284 


.263 


.276 


.266 


3 


.22942 


•259 


•259 


.244 


.252 


.250 


4 


.20431 


.238 


.238 


.225 


.232 


•234 


5 


.18194 


.220 


.220 


.207 


.212 


.219 


6 


.16202 


.203 


.203 


.192 


.192 


.203 


7 


.14428 


• l80 


.180 


.177 


.176 


.188 


8 


.12849 


.165 


.165 


.l62 


.160 


.172 


9 


•II443 


.148 


.148 


.148 


.144 


.156 


10 


.IOI89 


•134 


•134 


•135 


.128 


.141 


ii 


.O9074 


.120 


.120 


.120 


.Il6 


•125 


12 


.08081 


.109 


.109 


• 105 


.104 


.IO9 


13 


.07I99 


•095 


•095 


.092 


.092 


.0938 


14 


.06408 


.083 


.083 


.080 


.080 


.0781 


15 


.05706 


.072 


.072 


.072 


.072 


.0703 


16 


.O5082 


.065 


.065 


.063 


.064 


.0625 


17 


.O4525 


.058 


.058 


•054 


.056 


.0563 


18 


.04030 


.049 


.O49 


.047 


.O48 


.0500 


19 


.03589 


.040 


.042 


.041 


.040 


.0438 


20 


.O3196 


.035 


•035 


•035 


.O36 


•0375 


21 


.O2846 


.0315 


.032 


.032 


.032 


.0344 


22 


.025347 


.0295 


.028 


.028 


.028 


•0313 


23 


.022571 


.027 


025 


.025 


.024 


.0281 


24 


.0201 


.025 


.022 


.023 


.022 


.0250 


25 


.OI79 


.023 


.020 


.020 


.020 


.0219 


26 


.OI594 


.0205 


.018 


.018 


.Ol8 


.0188 


27 


.OI4I95 


.OI875 


.Ol6 


.017 


.O164 


.0172 


28 


.OI264I 


.OI65 


.014 


.Ol6 


.OI48 


.OI56 


29 


.OII257 


•0155 


.013 


.015 


.OI36 


.0141 


30 


.OIOO25 


•OI375 


.012 


.014 


.OI24 


.0125 


3i 


.008928 


.OI225 


.010 


.0135 


.OIl6 


.0109 


32 


.0O795 


.OII25 


.009 


.013 


.OIO8 


.0102 


33 


.OO708 


' .OI025 


.008 


.Oil 


.OIO 


.0094 


34 


.O063 


.0095 


.007 


.010 


.0092 


.0086 


35 


.OO561 


.009 


•005 


.0095 


.OO84 


.OO78 


36 


.0O5 


.0075 


.004 


.OOQ 


.OO76 


.0O70 


37 


.OO445 


.OO65 




.0085 


.OO68 


.O066 


38 


.OO3965 


. .00575 




.008 


.006 


.0063 


39 


.00353I 


.005 




.0075 


.0052 




40 


.003144 


.0045 




.007 


.OO48 





MOTION PICTURE ELECTRICITY 243 

EQUIVALENTS OF ELECTRICAL UNITS 
(Hering) 

i kilowatt = 1,000 watts. 

I kilowatt = 1.34 h. p. 

1 kilowatt = 44,257 foot-pounds per minute. 

1 kilowatt = 56.87 B. t. u. per minute. 

1 horse power = 746 watts. 

1 horse power = 33,000 foot-pounds per minute. 

1 horse power = 42.41 B. t. u. per minute. 

1 B. t. u. (British Therman Unit) = 778 foot-pounds. 

1 B. t. u. = 0.2930 watt-hr. 

TO FIND AMPERES PER PHASE 
Three-Phase Circuits 





POWER 


FACTOR 






VOLTS 


IOO% 


90% 


80% 


70% 


no 


Kw X 5.256 


5.84 


6-57 


7-5i 


220 


Kw X 2.628 


2.92 


3.28 


3-75 


370 


Kw X 1.562 


1-735 


1.952 


2.231 


380 


Kw X 1. 521 


I.69O 


1.900 


2.170 


390 


Kw X 1482 


I.646 


1.852 


2.117 


440 


Kw X 1.314 


I.460 


I.64O 


1-877 


550 


Kw X 1.050 


I.I66 


I.3I2 


1.500 


1 100 


Kw X .5256 


.584 


.657 


•751 


2200 


Kw X .2628 


.292 


.328 


•375 


2400 


Kw X .2400 


.266 


.3000 


•342 


3300 


KwX .1750 


.1944 


.2187 


.250 


6600 


KwX .0875 


.0972 


.IO93 


.125 


1 0000 


KwX .0578 


.064O 


.0722 


.0825 


13200 


KwX .0438 


.048b 


.0546 


.0625 


16500 


Kw X .0350 


.0388 


•0437 


.0500 


22000 


Kw X .0263 


.0292 


.O328 


•0375 


33000 


KwX .0175 


.0194 


.0219 


.0250 



Two-Phase Circuits 



no 


Kw X 4-54 


5.04 


5.67 


6.48 


220 


Kw X 2.27 


2.52 


2.83 


3-24 


440 


KwX 1.13 


1.26 


1. 41 


1.62 


iroo 


KwX -454 


.504 


.567 


.648 


2200 


Kw X .227 


.252 


.283 


•324 



244 MOTION PICTURE ELECTRICITY 

Single-Phase Circuits 



no 


Kw X 9.09 


10.01 


11.36 


12.98 


220 


Kw X 4-54 


5-05 


5-68 


6.49 


440 


Kw X 2.27 


2.52 


2.84 


3-24 


1 100 


KwX .909 


I.OI 


1. 136 


1.298 


2200 


KwX 454 


•505 


.568 


.649 



CURRENT PER PHASE IN VARIOUS SYSTEMS 

W 



P.F. 



for single-phase circuit. 



W 

1 = 0.50 X for two-phase circuit. 

E X P.F. 

W 

1 == 0.58 X for three-phase circuit. 

E X P.F. 

1 = Current in line in amperes ; W = energy delivered in watts ; 
E = potential between mains in volts ; P.F. == power factor. When 
power factor cannot be accurately determined it may be assumed 
as follows : Lighting load with no motors, 0.95 ; lighting load 
and motors, 0.85 ; motors only, 0.80. 

TABLE OF SPECIFIC RESISTANCE 
(Foster) 

SPECIFIC 

RESISTANCE IN 

MICROHMS 

PER RELATIVE 

SUBSTANCE CUBIC INCH CONDUCTANCE 

Copper (annealed) 1.57° 100 

Copper (hard) 1,603 98.1 

Silver (annealed) i,49 2 105 

Silver (hard) 1,620 98 

Gold 2,077 . 76 

Aluminum (annealed) 2,889 54 

Platinum 8,982 17 

Iron (pure) 9,628 16 

Iron (telegraph wire) 15. 10 

Lead , 1963 8,3 

Mercury 94-34 x -6 



MOTION PICTURE ELECTRICITY 



245 



COMPARATIVE RESISTANCE OF VARIOUS 
METALS 



Copper i 

Aluminum 1.5 

No. 5 Alloy 2 

Platinum 6 

Norway Iron .... 7 

Pure Nickel 7 



Soft Steel 8 

No. 15 Alloy 12 

"Ferro-Nickel" .. 17 

18% Ger. Silver. . 19 

"Yankee Silver".. 20 

"Therlo" 27 



30% Ger. Silver.. 28 

"Advance" 28 

"Climax" 50 

"Nichrome" 60 

"Nichrome II" ... 66 



COLORS OF SOURCES OF LIGHT 



SOURCE 

High sun 
Electric arc, short 
Electric arc, long 
Nernst glower 
Tungsten filament 
Carbon filament 
Mercury arc 



COLOR 

White 

White 

Blue-white to violet 

White to yellowish white 

Nearly white 

Yellowish white 

Blue-green 



The foregoing comparative figures giving the bril- 
liancy of various illuminants show the tremendous advan- 
tage of the electric arc for projecting purposes. In fact 
there is no substitute for the electric arc at the present 
time, although calcium light can be used in case of neces- 
sity for traveling exhibits. 

BRIGHTNESS OF VARIOUS ILLUMINANTS 



SOURCE 


C.P. PER SQ. IN. 


NOTES 


Sun (in zenith) 


600,000 


Necessarily rough 
estimate 


Electric arc 


10,000 to 100,000 


Reaching often 200,000 
in the crater of a very 
powerful arc 


Calcium light 


5,000 




Nernst glower 


1,000 




Incandescent 




Depending on efficiency, 


lamps 


200 to 500 


some metallic filament 
lamps run above 1,000 



The above table is of great interest because it shows 
the value of maintaining an electric arc short when used 
for projection. Only by maintaining the arc short is it 
possible to secure a white light. Whenever the arc is 



246 MOTION PICTURE ELECTRICITY 

maintained long, the light becomes blue-white to violet 
and is much inferior for projection purposes. As a mat- 
ter of fact, the only way of getting an illumination which 
is equal in quality to the high sun is obtained by an electric 
arc between pure carbon points maintained short. 

TABLE OF REFLECTION COEFFICIENTS 

Material Coefficient Material Coefficient 

Polished silver 92 to 93 Yellow cardboard 30 

Mirror silvered on back. . .82 to 88 Light blue cardboard 25 

White blotting paper 82 Brown cardboard 20 

White cartridge paper 80 Yellow painted wall, dirty.. 20 

Polished brass 70 to 75 Emerald green paper 18 

Mirror backed with Amal- Dark brown paper 13 

gam 70 Vermilion paper 12 

Ordinary foolscap paper... 70 Bluish green paper 12 

Chrome-yellow paper 62 Cobalt blue paper 12 

Orange paper 50 Black paper 5 

Yellow wall paper 40 Ultramarine blue paper.... 3.5 

Yellow-painted wa!l 40 Black velvet 4 

Light pink paper 36 

The light reflected from a surface in per cent, of the 
total light falling upon that surface is called the reflection 
coefficient. 

A careful perusal of the figures in the above table 
brings out the important point that a surface similar to 
a common white blotting paper possesses almost as much 
reflective power as a mirror silvered on the back. These 
figures have been carefully prepared by a special com- 
mittee of the National Electric Light Association and may 
be absolutely relied upon. The figures would indicate 
that a pure white screen, by that I mean a screen with a 
surface which is not glossy, makes about the best arrange- 
ment for picture projection. A plastered wall having a 
dull white surface, or possibly if coated with some of the 
special compounds tinting toward a grayish blue will make 
a splendid screen upon which to project motion pictures. 
The pictures on such a screen stand out in better relief 
than if a polished or metallic surface is used, and besides 
the flicker is cut down to a minimum. 

This table is also of great benefit to the exhibitor who 
is arranging for the ornamentation of the interior of a 
picture theater, because it is a positive guide as to the 



MOTION PICTURE ELECTRICITY 247 

various reflective powers of the different color schemes. 
You will, of course, keep in mind that for the decoration, 
those colors which have the lowest reflection coefficient 
should be selected, and it is interesting to know that the 
browns and greens are of exceptional value in this respect. 

ENERGY RADIATION 

When a body is heated above the surroundings, it radi- 
ates energy ; at first in the form of heat, and later, when 
certain wave lengths are reached, a portion of the radiant 
energy is in the form of light. Electric energy is easily 
applied to bodies whose temperature it is desired to raise 
to a point where they become incandescent and give off 
light. In an electric lamp the electric energy is com- 
pletely transformed into heat, a large portion of which is 
given off as radiant energy. Part of the radiations are 
visible and constitute light; however, a comparatively 
small proportion of the total energy is given off in this 
form. The maximum radiation energy approaches visible 
radiation more and more as the temperature of the radiat- 
ing body is increased. It is by increasing the temperature 
of the filament that its specific consumption in watts per 
candle power is decreased, and this is why high efficiency 
lamps have shorter lives than the less efficient lamps of 
the same kind. The maximum possible efficiency would 
be reached at a temperature of about 6800 degrees centi- 
grade, which no known solid will endure. As a matter of 
fact, the usual temperature at which the filament of an 
incandescent lamp is worked lies between 1550 and 1600 
degrees centigrade. 

ELECTRIC SIGNS 

There are many kinds of electric signs ; some flash out 
and in and others seem to be written with an invisible 
hand. Occasionally the inscriptions appear sentence by 
sentence or word by word. There are signs in the form 
of emblems, trademarks, flags, eagles, etc., studded with 
sockets ; live borders for signs, such as crawling serpents, 



248 MOTION PICTURE ELECTRICITY 

jumping grasshoppers or rabbits, but the most popular 
form of electric sign gives a steady illumination with 
white or colored lamps ; the letters may be interchangeable 
so as to alter the reading occasionally if desired. An elec- 
tric sign should be considered as an advertising invest- 
ment, and if the impression it makes is not a good one, 
the money invested in it is worse than thrown away. It 
should lend a distinguishing air of quality to a theater and 
it is this element which gives it its greatest value. While 
a sign will designate a place of business, and perhaps the 
nature of that business, a large part of its value lies in the 
impression it makes. Hence only the best and most per- 
manent types of sign should be adopted, no matter how 
small they must be, to meet the price the customer can 
afford to pay for one. 

Some of the essentials of a good sign are that it should 
be made of the very best materials, carefully put together 
and simple in construction, so that it may be very durable. 
It must be waterproof and have a surface preferably of 
enameled metal that will not fade or lose its color. Me- 
chanical arrangements for its suspension must be such 
that it is rigidly and safely supported, not only actually, 
but in appearance. 

Turning from such generalities as the preceding with 
the assumption that electric signs are of great value as 
advertising mediums, it will be well to consider more in 
detail what the actual cost of electric advertising will be. 

The reading on a sign should be made as brief as pos- 
sible and large letters should be employed, spaced well 
apart. Raised letters are more effective than flush let- 
ters, standing out much more prominently both day and 
night. When signs are placed flat against a building, 
grooved letters should be used, as they show more plainly 
and need fewer lamps. 

The price of an electric sign naturally depends upon 
the number and size of the letters required and the num- 
ber of lamps necessary to illuminate them. The price for 
a single letter illuminated by the minimum number of 
lamps required to give a good effect, ranges, on an aver- 
age, from $6 to $12 a year according to the height of the 



MOTION PICTURE ELECTRICITY 249 

letters. The following table will enable the reader to 
make a fairly accurate calculation as to the price for 
which a satisfactory sign can be obtained: 

COST OF ELECTRIC SIGNS 

Of standard block style letters, made of metal on a full 
metal background Japan-enameled. 



HEIGHT 


AVERAGE 


NUMBER OF LAMPS 




OF LETTERS 


PER LETTER 


PRICE PER LETTER 


IN INCHES 


RAISED 


GROOVED 


DOLLARS 


IO 


6 


4 


6.20 


12 


8 


6 


6.8o 


H 


8 


6 


7.00 


16 


10 


8 


7.60 


18 


10 


8 


7.90 


20 


10 


8 


8.20 


24 


12 


IO 


9.40 


30 


14 


IO 


10.70 


36 


16 


12 


12.80 



Signs with flush letters would be about 20% less ex- 
pensive, while any special style of letter, such as the old 
English or pointed block would be from 2.5% to 20% 
higher. The prices indicated in the table do not, of 
course, include extras such as non-electric lettering or 
special ornamentation. Neither do they include the cost 
of material for hanging the sign, or of wiring for writing 
or spelling flashers. But even then these figures work out 
at a great deal less than, the sum that many people imagine 
must be spent for an electric sign. The same thing also 
applies to the cost of operation — it is far less formidable 
than is generally supposed. For example, if a sign con- 
tains 4 c.p. lamps, it takes 50 lamps to make up a kilowatt 
of capacity and if it contains 2 c.p. lamps, it takes approx- 
imately 80 to make up a kilowatt. Multiply its capacity 
in kilowatts by the number of hours during which the sign 
will burn each night and the nightly consumption of en- 
ergy in kilowatt-hours is thus obtained. Knowing the 
rate charged for energy, it is easy to multiply the number 
of kilowatt-hours by the rate, and thus get the nightly 
cost of signs containing various numbers of lamps. 



250 



MOTION PICTURE ELECTRICITY 



COST OF OPERATING AN ELECTRIC SIGN 
PER HOUR 

At the rate of 10 cents per kilowatt-hour, using 4 or 
2 c.p. lamps. 

Average efficiency carbon filament lamps. 

4 C.P. LAMPS 2 C.P. LAMPS 

NUMBER OF LAMPS COST PER HOUR COST PER HOUK 

IN SIGN CENTS CENTS 

25 5 3 

.50 10 6 

75 15 9 

100 20 12 

150 30 18 

200 40 24 

Note — If Tungsten or Mazda lamps are used, current 
cost is 50 to 70% lower. Average number of hours burn- 
ing per month, 75 to 150. 

If the cost of illuminating a sign is compared with the 
cost of advertising in a local paper, the comparison will 
be found to be in favor of the sign, especially as it points 
out the exact position of the theater and attracts people 
to it. 

COMPARISON OF LIGHT 

Given for same cost per 1,000 hours — 100- Watt Tung- 
sten and 100- Watt carbon lamps; and saving for equal 
light. 

TUNGSTEN CARBON CARBOU 

1-100 1-100 2.48-100 

WATT WATT WATY 

1.20 2.97 2.9; 

W.P.C. W.P.C. W.P.C. 

Candle power 83.3 33.6 83.3 

Average cost of lamps 1.04 .24 .595 

Average life of lamps 1,000 600 600 

Renewal cost per 1,000 hours 1.04 .40 .0917 

Power consumed per 100 hours 

k.w.h 100. 100. 248. 

Cost of power at 5 cts '. 500 5.00 12.40 

Cost of power at 10 cts 10.00 10.00 24.80 

Cost of renewals and power at 5 cts. 6.04 5.40 13.39 

Cost of renewals and power at 10 cts. 11.04 10.40 25.79 

Comparison of light for same cost. . 100% 42.8% 42.8% 

% saving for S 5 cts 55 0.0 

equal light 1 10 cts 57 °-° 



MOTION PICTURE ELECTRICITY 251 

This makes an average saving of 56 per cent, in the cost for 
lamp renewals and power, in addition to which there is a saving 
effected in the cost for wiring by the reduction pi the number of 
outlets, the quantity of material, and the reduction of the load. 

FANS AND BLOWERS 

To procure fresh air and to keep it in circulation is a 
problem of particular interest to those who are compelled 
to be either temporarily or permanently indoors. In sum- 
mer, especially, and in inland and low sections of the 
country, arrangements for good ventilation become a mat- 
ter of business necessity to render a theater, store, shop, 
or factory even habitable during the hot months, and in 
the winter it is an equally important matter where a large 
number of people congregate. 

For such ventilation it is not only necessary to draw 
in pure air, but to remove the vitiated air, and to continue 
this process indefinitely. For many industrial purposes, 
however, the desired object is to remove moist air from 
the rooms in which lumber, cloth, paper, tobacco, or other 
articles of merchandise are being dried, to exhaust from 
the rooms those noxious gases or fumes which attend 
certain processes of manufacture or to cause a circulation 
of air over heated or cooled pipe coils for maintaining 
equable temperature in assembly rooms or apartments. 
Though this was not formerly an easy matter to accom- 
plish, apparatus is now obtainable which will readily pro- 
duce the required results. 

A ventilating fan of the propeller type is usually fixed 
in a circular aperture in the wall and can be arranged as 
desired — either to draw in fresh air or expel bad air. An 
exhaust fan should be placed so that it discharges the air 
in the same direction as the prevailing wind, in order to 
avoid having to contend with wind pressure. The num- 
ber and location of air inlets and probable effects of pre- 
vailing air currents should also be considered carefully 
in determining the place for the fan. Under ideal con- 
ditions the room to be ventilated should have only one in- 
let for air which should be at the opposite end of the 
room from the exhaust fan. The size of the fan to be 
installed, of course, depends upon local conditions, but 



252 MOTION PICTURE ELECTRICITY 

roughly speaking, the 18 in. size will be found sufficient 
to provide fresh air for 25 to 30 persons. This allows for 
the provision of 2,000 cubic feet of air per hour for each 
occupant of the room. 

. APPROXIMATE PRICES FOR FANS 
Alternating Variable Speed Exhaust Fans 

1 10 or 220 Volts as Specified 

At ioc 

rate 

per hour 

cost of 

opera- Revolu- Cubic 

Watts tion tions feet of 

per at full per air per 

HP. hour speed Size Cycle minute minute Price 

Non-reversible 

without speed j i-io 45 y 2 c. 12 60 1500 750 $16.00 
regulator ....( l / & 85 %c. 16 60 1500 1,300 20.00 
With speed regu- 
lator non-re- 
versible 1-6 150 ij^c. 18 60 80 to 800 2,500 72.00 

Reversible with 
speed regu- 
lator l / 2 400 4 c. 24 60 80 to 750 6,000 100.00 

Reversible with 
speed regu- 
lator 1 800 8 c. 30 60 80 to 700 12,800 165.00 

Reversible with 
speed regu- 
lator (for 220 
volts only)... \y 2 1200 12 c. 36 60 80 to 650 17,300 225.00 

Direct Current Exhaust Fans 

For direct-current circuits, ioo to 230 volts, the venti- 
lating exhaust fans possess all the advantages above de- 
scribed for the alternating fans, except that they are not 
made reversible. 

At ioc rate 
per hour, Revo- 
Watts cost of op- lutions Cubic feet 
per eration at per of air per 
H.P. hour full speed Size minute minute Price 
Without speed (1-10 45 y 2 c. 12 1500 1,000 $16.00 
regulator . .( l /i 85 Yt,c. 16 1200 1,600 20.00 
With speed regu- 
lator yi 200 2 c. 18 1000 4,060 75.00 

With speed regu- 
lator y 2 400 4 c. 24 850 7,620 100.00 

With speed regu- 
lator Vi, 600 6 c. 30 640 12,400 125.00 

With speed regu- 
lator i z A iooo 10 c. 36 525 18,000 165.00 



MOTION PICTURE ELECTRICITY 



253 



The foregoing data of exhaust fans for alternating and 
direct current is intended to be used as a guide. The cost 
of operating may vary slightly for various makes of fans 
and the cost prices given are only approximate, also sub- 
ject to variation depending upon the make and style of 
fan wanted. 

WEIGHTS AND MEASURES 



Troy Weight 



12 ounces 



24 grains = 1 pwt. 

20 pwt. = 1 ounce 

Used for weighing gold, silver and jewels. 



= 1 pound 



Apothecaries' Weight 

20 grains = 1 scruple 8 drams = 1 ounce 

3 scruples = 1 dram 12 ounces = 1 pound 

The ounce and pound in this are the same as in Troy weight. 

Avoirdupois Weight 



27V3 grains 
16 drams 
16 ounces 
25 pounds 


= 1 dram 4 quarters 
= 1 ounce 2,000 lbs. 
= 1 pound 2,240 lbs. 
= 1 quarter 

Dry Measure 


— 


1 cwt. 

1 short ton 

1 long ton 


2 pints 
8 quarts 


= 1 quart 4 pecks 
= 1 peck 36 bushels 

Liquid Measure 


= 


1 bushel 
I chaldron 


4 gills 
2 pints 
4 quarts 


= 1 pint 31^2 gallons 
= 1 quart 2 barrels 
= 1 gallon 

Long Measure 


= 


1 barrel 
1 hogshead 


12 inches 
3 feet 
S l /2 yards 


= I foot 40 rods 
= 1 yard 8 furlongs 
= 1 rod 3 miles 

Square Measure 


= 


1 furlong 
1 sta. mile 
1 league 


144 sq. in. 
9 sq. ft. 
30/4 sq. yds. 


= 1 sq. ft. 40 sq. rods 
= 1 sq. yd. 4 roods 
= 1 sq. rod 640 acres 


= 


1 rood 
1 acre 
1 sq. mile 



254 



MOTION PICTURE ELECTRICITY 





Surveyors' 


Measure 


7.92 inches 


— 


1 link 




25 links 


= 


1 rod 




4 rods 


= 


1 chain 


10 sq. chains or 160 i 


q. rds. = 


1 acre 




640 acres 


= 


1 sq. mile 


36 sq. miles (6 miles 


; sq.) = 


1 township 




Cubic Measure 




1,728 cubic in. 


= 


1 cu. : 


ft. 


27 cu. ft. 


= 


1 cu. ; 


rd. 


128 cu. ft. 


r= 


1 cord 


. (wood) 


40 cu. ft. 


— 


1 ton 


(shpg) 


2,150.42 cubic inches 


= 


1 standard bushel 


231 cubic inches 


= 


1 U. S. standard gallon 


1 cu. ft. 


~ 


about Y$ of a bushel 


Metric Equivalents 


— Linear Measure 


1 centimeter 


= 


o.3937 


in. 


1 in. 


== 


2.54 


centimeters 


1 decimeter (3.937 in.) = 


0.328 


ft. m 


1 ft. 


— 


3.048 


decimeters 


1 meter (39-37 : 


in.) 


1.0936 


yards 


1 yd. 


rr 


0.9144 


meter 


1 dekameter 


^r 


1.9884 


rds. 


1 kilometer 


= 


0.62137 


m. 


1 rd. 


— 


0.5029 


dekameter 


1 m. 


= 


1.6093 


kilometers 




Square Measure 




1 sq. centimeter 


= 


0.1550 


sq. in. 


1 sq. decimeter 


r= 


0.1076 


sq. ft. 


1 sq. meter 


= 


1. 196 


sq. yd. 


1 are 


zz 


3-954 


sq. rds. 


1 hectare 


= 


2.47 


acres 


1 sq. kilometer 


= 


0.386 


sq. m. 


1 sq. in. 


— 


6.452 


sq. centimeters 


1 sq. ft. 


= 


9.2903 


sq. decimeters 


1 sq. yd. 


= 


0.8361 


sq. meter 


1 sq. rd. 


= 


0.2529 


are 


1 acre 


= 


0.4047 


hectare 


1 sq. m. 


zz: 


2.59 


sq. kilometers 




Weights 




I gram 


= 


0.03527 


ounce 


I kilogram 


= 


2.2046 


lbs. # 


1 metric ton 


= 


1.1023 


English tons 


1 ounce 


= 


28.35 grams 


1 lb. 


= 


0.4536 kilogram 


1 English ton 


= 


0.9072 


metric ton 



MOTION PICTURE ELECTRICITY 



255 



Approximate Metric Equivalents 

i decimeter = 4 in. 

1 meter = 1.1 yds. 

1 kilometer = ^ of a mile 

1 hectare = 2 $4 acres 

1 stere, or cu. meter = z /i of a cord 

1 liter = 1.06 qts. liquid, 0.9 qt. dry 

1 hektoliter = 2 l A bus. 

I kilogram = 2Y$ lbs. 

I metric ton = 2,200 lbs. 



STRENGTH OF MATERIALS 



MATERIALS 

Alum. Bronze, 10% Alum. . . 
Alum. Bronze, 1%% Alum. . 

Brass, Cast 

Brass, Wire 

Bronze or Gun Metal 

Copper, Cast 

Sheet 

Wire 

Iron, Cast 

Wrought 

Lead, Sheet 

Steel, Cast 

Rivet 

Axle 

Wire 

Boiler = 

Soft Open Hearth... 

Brickwork, Ordinary 

Cement 

Cement, Portland, I to 1, 

Neat 

Granite and Limestone 

Sandstones 

Glass (Common) 

Ash (Wood).... 

Hemp Ropes 

Hickory 

Oak (White) 

Pine (Yellow) 

Chestnut 

Locust 

Spruce 



TENSILE STRENGTH 
POUNDS 
PER SQ. IN. 
85,000 
28,000 
22,000 

49,000 
36,000 
19,000 
30,000 

49,000- 67,000 
13,400- 29,000 
46,000- 54,000 
3,300 

61,000-120,000 
50,000- 60,000 
75,000- 90,000 
200,000-240,000 
55,000- 65,000 
52,000- 62,000 



550- 650 



4,800- 
11,000- 
12,000- 
12,800- 
10,000- 
12,000- 
10,500 
20,000- 
10,000- 



17,000 
16,000 
18,000 
20,000 
19,200 

25,000 
19,500 



COMPRESSIVE 
STRENGTH 

POUNDS 
PER SQ. IN. 



10,300 



82,000-145,000 
36,000- 40,000 



300- 
450- 



500 
1,000 



5,000- 10,000 
8,000- 25,000 
6,000- 10,000 
20,000- 40,000 
4,400- 9,400 

8,900 

4,600- 9,500 
5,400- 9,500 
5,350- 5,600 
9,100- 11,700 
5,000- 7,800 



256 MOTION PICTURE ELECTRICITY 



CENTIGRADE AND FAHRENHEIT SCALES 



CENTIGRADE 


FAHRENHEIT 


CENTIGRADE 


FAHRENHEIT 


O 




32 




50 


122 


5 




4i 




55 


131 


10 




50 




60 


140 


15 




59 




65 


149 


20 




68 




70 


158 


25 




77 




75 


167 


30 




86 




80 


176 


35 




95 




85 


185 


38 




100.4 




90 


194 


40 




104 




95 


203 


42 




107.6 




100 


212 


45 




113 










Temp 


. C = 


5/9 


(Temp. F — 32) 






Temp, 


, F = 


9/5 


(Temp. C + 32) 





EFFECT OF HEAT ON MATERIALS 



MELTING POINT 
FAHRENHEIT 

Mercury — 39 

Tin 442 

Bismuth 507 

Lead 617 

Zinc 773 

Antimony 1,150 

Aluminum 1,157 

Bronze 1,692 

Silver 1,873 

Copper 1,996 

Gold 2,016 

Cast Iron, Gray 2,786 

Steel 2,372 to 2,552 



MOTION PICTURE ELECTRICITY 257 



HIGH TEMPERATURES JUDGED BY COLOR 

(Kent) 

v The temperature of a body can be approximately judged by 
the experienced eye unaided, and M. Pouillet has constructed a 
table which has been generally accepted, giving the colors and 
their corresponding temperatures as below: 

m COLOR DEC C DEC F 

Incipient red heat 525 977 

Dull red heat 700 1,292 

Incipient cherry-red heat 800 1,472 

Cherry-red heat 900 1,652 

Clear cherry-red heat 1,000 1,832 

Deep orange heat 1,100 2,021 

Clear orange heat 1,200 2,192 

White heat 1,300 2,372 

Bright white heat 1,400 2,552 

Dazzling white heat 1,500 2,732 

to to 

1,600 2,912 



258 



MOTION PICTURE ELECTRICITY 



HEAT UNITS 
(Foster) 



i Kw-hr. = 



1,000 watt-hr. 

1.34 h.p.-hr. 

2,654,200 ft.-lb. 

3,600,000 joules. 

3,412 heat-units. 

367,000 kg-m. 

.235 lb. carbon oxidized with perfect 

efficiency. 
3.53 lb. water evap. from and at 212 F. 
22.75 lb. of water raised from 6o° to 

212° F. 



1 h.p.-hr = 



f .746 kw-hr. 
1,980,000 ft.-lb. 
2,545 heat-units. 
273,740 kg-m. 
.175 lb. carbon oxidized with perfect 

efficiency. 
2.64 water evaporated from and at 212 ° F. 
17.0 lb. water raised from 62 ° F. to 

212° F. 



1 lb. carbon oxi- 
dized with per- 
fect efficiency 



14.544 heat units. 
1. 1 1 lb. anthracite coal oxidized. 
2.5 lbs. dry wood oxidized. 
21 cu. ft. illuminating gas. 
4.26 kw-hr. 
5.71 h.p.-hr. 
11,315,000 ft.-lb. 

15 lb. of water evaporated from and at 
212° F. 



1 lb. water evap- 
orated from and 
at 212 F. 



.283 kw.-hr. 
.379 h.p.-hr. 
965.7 heat units. 
103,900 kg-m. 
1,019,000 joules. 
751,300 ft.-lb. 
(^ .0664 of carbon oxidized. 



MOTION PICTURE ELECTRICITY 259 



HEATING VALUES FOR LIQUID FUELS 
(Gill) 



SP. GR. 

76 deg. Gasoline.. 76.5 

62 deg. Naphtha.. 61.0 
135 deg. Fire T 

Kerosene 48.0 

150 deg. Fire T 

Kerosene 48.0 

Beaumont Crude.. 0.924 

California 0.966 

Cal. and Texas 0.966 

Pennsylvania 0.886 

Wyoming 0.996 

Residuum, Va. ... L. 860 
Residuum, Rus'n . . 0.884 







HEAT VALUE 




FLASH 


FIRE 


B. T. U. 




DEG. F. 


DEG. F. 


PER LB. 


SP. HEAT 






18,080 


0.55 


... 


... 


I7,86o 


O.50 


its 


135 


I7,8lO 


0.50 


134 


150 


l8,290 


O.49 


180 


200 


I9.O60 




230 


311 


18,667 




270 


280 


19,215 
19,224 
19,668 
19,200 
19,926 





260 



MOTION PICTURE ELECTRICITY 



WEIGHT OF MATERIALS AND LIQUIDS 



WEIGHT OF 

ONE CUBIC 

FOOT POUNDS 

Platinum 1,342 

Gold 1,200 

Mercury, fluid 849 

Lead, wire 704 

Silver . 655 

Bismuth 617 

Copper, sheet 549 

Copper, wire 554 

Bronze 544 

Nickel, cast 516 

Brass, cast 505 

Brass, wire 533 

Steel 4896 

Iron, wrought ?. . . . 480 

Iron, cast 450 

Tin 462 

Zinc, sheet 449 

Antimony 418 

Aluminum, wrought 167 

Aluminum, cast 160 

Magnesium 108.5 

Sulphuric Acid 1 14.9 

Nitric Acid 76.2 

Pure Water 62.425 

Oil, linseed 58.7 

Oil, turpentine 54.3 

Petroleum 54.9 

Naphtha 53.1 

Ether, sulphuric 44.9 

Benzine 53.1 



SPECIFIC GRAVITY 
WATER = I 
21.522 
19.245 
13.596 
11.282 
IO.505 

9.90 

8.805 

8.880 

8.73 

8.28 

8.IO 

8.548 

7.852 

7.698 

7.217 

7409 

7.20 

6.71 

2.67 

2.56 

1.74 

I.84 

1.22 

1. 000 

0.94 

O.87 

O.88 

0.85 

0.72 

O.85 



MOTION PICTURE ELECTRICITY 



261 



DECIMALS OF AN INCH FOR EACH ONE 
SIXTY-FOURTH 



32DS 


64.THS 


DECIMAL 


FRACTION 


32DS 


64THS 


DECIMAL 


FRACTION 




1 


.OI5625 






33 


.515625 




I 


2 


.03125 




17 


34 


.53125 






3 


.O468/5 






35 


.546875 




2 


4 


.0625 


l/l6 


18 


36 


.5625 


9/16 




5 


.078I25 






37 


.578125 




3 


6 


•09375 




19 


38 


•59375 






7 


•109375 






39 


.609375 




4 


8 


.125 


Vs 


20 


40 


.625 


H 




9 


.I40625 






4i 


.640625 




5 


10 


.15625 




21 


42 


.65625 






11 


.I71875 






43 


.671875 




6 


12 


.1875 


3/l6 


22 


44 


.6875 


11/16 




13 


.203125 






45 


.703125 




7 


14 


.21875 




23 


46 


.71875 






15 


•234375 






47 


•734375 




8 


16 


•25 


y 4 


24 


48 


•75 


M 




17 


.265625 






49 


.765625 




9 


18 


.28125 




25 


SO 


.78125 






19 


.296875 






51 


.796875 




10 


20 


•3125 


5/16 


26 


52 


.8125 


13/16 




21 


.328125 






53 


.828125 




ii 


22 


•34375 




27 


54 


.84375 






23 


•359375 






55 


.859375 




12 


24 


•375 


Vi 


28 


56 


.875 


% 




25 


.390625 






57 


.890625 




13 


26 


.40625 




29 


58 


.90625 






27 


.421875 






59 


■921875 




14 


28 


•4375 


7/16 


30 


60 


•9375 


15/16 




29 


.453125 






61 


.953125 




15 


30 


.46875 




31 


62 


.96875 






3i 


•484375 






63 


•984375 




16 


32 


•5 


% 


32 


64 


1. 


1 



262 



MOTION PICTURE ELECTRICITY 



TABLE FOR FILM PROJECTION 
Aperture Opening, 11/16 x 15/16 



Equiv. 
Focus 








Distance from '. 


Film to Screen 










in 


15 


20 


25 


30 


35 


40 


45 


50 


60 


70 


80 


90 


100 


inches 


ft. 


ft. 


ft. 


ft. 


ft. 


ft. 


ft. 


ft. 


ft. 


ft. 


ft. 


ft. 


ft. 


2 


S.i 


68 


8.5 


10.3 


12.0 


13.7 


15-4 


17.1 


20.6 


24.0 


27.5 


30.8 


34-3 




7.0 


9-3 


11.6 


14.0 


16.4 


18.7 


21. 1 


23-4 


29.4 


32.7 


37-4 


42.1 


46.8 


2% 


4.8 


6.4 


8.0 


9.6 


ii-3 


12.9 


14-5 


16.1 


19.4 


22.6 


25.8 


28.9 


32.3 




6-5 


8.7 


11. 


13-2 


15.4 


17.6 


19.8 


22.0 


26.4 


30.8 


35-2 


39-3 


44.0 


2V* 


4-5 


6.1 


7-6 


9-i 


10.6 


12.2 


13.7 


15.2 


18.3 


21.3 


24.4 


27.2 


30.5 




6.2 


8.3 


10.3 


12.4 


14-5 


16.6 


18.7 


20.8 


24.9 


29.1 


33-2 


37-2 


41.6 


2 l /2 


4-1 


5-4 


6.8 


8.2 


9.6 


10.9 


12.3 


13.7 


16.4 


19.2 


22.0 


24.5 


27.4 




5-6 


7-4 


9-3 


11. 2 


13.1 


14.9 


16.8 


18.7 


22.4 


26.2 


29.9 


33-4 


37-4 


2 34 


3-7 


4.9 


6.2 


7-4 


8-7 


9-9 


11. 2 


12.5 


15-0 


17.4 


20.0 


22.3 


24.9 




5-o 


6.7 


8.4 


10.2 


11.9 


13.6 


15-3 


17.0 


20.4 


23.8 


27.2 


30.4 


34.o 


3 


3-4 


4-5 


5-7 


6.8 


8.0 


9.1 


10.3 


11.4 


13-7 


16.0 


18.3 


20.4 


22.9 




4.6 


6.2 


7-7 


9-3 


10.9 


12.4 


14.0 


15.6 


18.7 


21.8 


24.9 


27.8 


31.2 


3 J A 


3-1 


4.2 


5-2 


6.3 


7-3 


8.4 


9-5 


10.5 


12.6 


14.8 


16.9 


18.9 


21. 1 




4-3 


5-7 


7-i 


8.6 


10. 


n-5 


12.9 


14.4 


17.2 


20.1 


23.0 


25.7 


28.8 


3H 


2.9 


3-9 


4.9 


5-8 


6.8 


7.8 


8.8 


9.8 


11. 7 


13.7 


15-7 


17.6 


19.6 




4.1 


5-3 


6.6 


8.0 


9-3 


10.6 


12.0 


13-3 


16.0 


18.7 


21.4 


24.0 


26.7 


3tt 


2.7 


3-6 


4-5 


5-4 


6.4 


7-3 


8.2 


9.1 


11. 


12.8 


14.6 


16.4 


18.3 




4.0 


4-9 


6.2 


7-4 


8.7 


9-9 


11. 2 


12.4 


14.9 


17.4 


19.9 


22.4 


24.9 


4 


2.6 


3-4 


4.2 


S-i 


6.0 


6.8 


7.7 


8.5 


10.3 


12.0 


13.7 


15.4 


17.1 




3-8 


4.6 


5-8 


7.0 


8.1 


9-3 


10.5 


11. 6 


14.0 


16.3 


18.7 


21.0 


23-4 


aVa 


2.4 


3-2 


4.0 


4.8 


5-6 


6.4 


7.2 


8.0 


9.6 


11. 3 


12.9 


14.5 


16.1 




3.6 


4-3 


5-4 


6.5 


7-6 


8.7 


9-8 


11. 2 


13-2 


15-4 


17.6 


19.8 


22.0 


A l A 


2.2 


3.o 


3-8 


4-5 


5-3 


6.2 


6.8 


7-7 


9-i 


10.6 


12.2 


13-7 


15.4 




3-4 


4.1 


5-1 


6.2 


7-2 


8.4 


9-3 


10.5 


12.4 


14.5 


16.6 


18.7 


21.0 


454 


2.0 


2.8 


3-6 


4-3 


5-0 


5-7 


6.5 


7.2 


8.6 


10. 1 


11. 5 


13.0 


14.4 




3-2 


3-9 


4-9 


5-8 


6.8 


7.8 


9.2 


9-8 


11. 8 


13-7 


15.7 


17.7 


19.7 


5 


1.9 


2.6 


3-4 


4.1 


4.8 


5-4 


6.1 


6.8 


8.2 


9.2 


10.9 


12.3 


13.7 




3-i 


3-7 


4.6 


5-5 


6.5 


7-4 


8.4 


9-3 


11. 2 


13.0 


14.9 


16.8 


18.7 


5J4 


1.8 


2-5 


3-2 


3-9 


4-5 


5-2 


5-8 


6-5 


7.8 


9-1 


10.4 


11. 7 


13.0 




2.9 


3-5 


4.4 


5-3 


6.2 


6.9 


8.0 


8.8 


10.6 


12.4 


14.2 


16.0 


17.8 


IV2 


1-7 


2.4 


3-i 


3-7 


4-3 


4-9 


5-6 


6.2 


7-4 


8.7 


9-9 


11. 2 


12.4 




2.8 


3-3 


4.2 


5.o 


5-9 


6.7 


7.6 


8.4 


10.2 


11.9 


13.6 


15.3 


17.0 


5 H 


1.6 


2.3 


2.9 


3-5 


4.1 


4-7 


5-3 


5-9 


7-i 


8.3 


9-5 


10.7 


11.9 




2.7 


3-2 


4.0 


4.8 


5-6 


6.4 


7-3 


8.1 


9-7 


- 1 1'3 


13-0 


14.6 


16.2 


6 


1-5 


2.2 


2.8 


3-4 


4.0 


4-5 


5-1 


5-7 


6.8 


8.0 


9-1 


10.3 


iz.4 




2.6 


3-i 


3-8 


4.6 


5-4 


6.2 


7.0 


7-7 


9-3 


10.9 


12.4 


14.0 


15.6 


•^ 














4-7 


5-2 


6.3 


7-3 


8.4 


9-6 


10.6 
















6.4 


7-1 


8.6 


10.0 


11.4 


13.0 


14-5 
















4.4 


4-9 


5-8 


6.8 


7-8 


8.8 


9-8 
















6.0 


6.6 


8.0 


9-3 


10.6 


12.0 


13.3 


7Va 
















4-5 
6.2 


5-4 
7-4 


6.4 
8.7 


7-3 
10. 


8.2 
11. 2 


9.i 
12.3 


8 


















S-i 
7.0 


6.0 

8.1 


6.8 
9-3 


7-7 
10.5 


8-5 
11.6 



Example — With a lens of 5^-inch focus at a distance of 35 ft., 
the screen image will be 4-3x5-9; at 40 ft., 5.6 x 7.6, etc. 



MOTION PICTURE ELECTRICITY 263 

TABLE FOR STEREOPTICON PROJECTION 
2j4 x 3 in. Mat Opening 

Equiv. Distance from Slide to Screen 

Focus 

in 15 20 25 30 35 40 45 50 60 70 80 90 100 

inches ft. ft. ft. ft. ft. ft. ft. ft. ft. ft. ft. ft. ft 

8 6.6 8.4 10.1 11. 8 13.5 15.2 17-0 20.4 

7.3 9.1 11. 12.9 14.8 16.6 18.5 22.3 
Sy 2 6.2 7.9 9-5 "- 1 I2 -7 14-3 16.0 19.2 

6.8 8.6 10.3 12.1 13.9 15-6 17-4 20.9 

9 5.9 7.4 8.9 10.5 12.0 13.5 15. 1 18.1 21. 1 

6.4 8.1 9.8 11. 4 i3-i 14.8 16.4 19-8 23.1 
9}4 5.6 7.0 8.5 9-9 n-4 12.8 14.2 17-1 20.0 

6.1 7.6 9.2 10.8 12.4 14.0 15.5 18.7 21.9 

10 5.3 6.6 8.0 9.4 10.8 12.2 13.5 16.3 19.0 21.8 

5.8 7.3 8.8 10.3 11. 8 13.3 14-8 17-8 20.8 23.8 

12 5.5 6.6 7.8 8.9 10. 1 11. 2 13.5 15.8 18.1 20.4 

6.0 7.3 8.5 9-8 11. 12.3 14.8 17.3 19.8 22.3 

14 5.6 6.6 7.6 8.6 9-6 11. 6 13.5 15-5 *7-5 *9-4 

6.2 7.3 8.3 9-4 10.5 12.6 14.8 16.9 i9-o 21.2 

i S 6.2 7.1 8.0 8.9 10.8 12.6 14.4 16.3 18.1 

6.7 7.7 8.7 9-7 ".7 13-7 15-7 *7-7 19-7 

16 5-8 6.6 7-5 8.4 10.1 11.8 13.5 15-2 17.0 
6.3 7.3 8.2 9.1 11.0 12.9 14.8 16.6 18.5 

17 5.4 6.2 7.0 7.8 9.5 11. 1 12.7 14.3 15.9 
,5.9 6.8 7.7 8.6 10.3 12.1 13.9 15.7 17.5 

18 5-1 5-9 6-6" 7-4 8.9 10.5 12.0 13.5 i5-i 
5.6 6.4 7.3 8.1 9.8 11.4 i3-i 14-8 16.4 

20 5.3 6.0 6.6 8.0 9-4 10.8 12.2 13.5 

5.8 6.5 7.3 8.8 10.3 11. 8 13.3 14.8 

22 5-4 6.0 7.3 8.5 9-8 11.0 12.3 

5.9 6.6 7-9 9-3 10.7 12.0 13.4 

24 5-5 6.6 7,8 8.9 10. 1 1 1.2 

6.0 7.3 8.5 9.8 11. o 12.3 

26 5-0 6.1 7.2 8.2 9.3 10.4 

5-5 6.7 7-9 9-0 10.1 11.2 

28 5-0 5-7 6.3 7.0 7.6 8.2 

5.5 6.2 6.9 7.7 8.4 9-1 



CALCIUM LIGHT 

This light is known by the names of Oxy-Hydrogen, 
Calcium, or Lime light, and is the most practical and sat- 
isfactory method of providing an intense light for magic 
lanterns and stereopticon illumination. Calcium light is 
produced by an incandescent surface on a piece of hard, 
unslaked lime, and is created by the combustion of a com- 
bination of oxygen and hydrogen gases. The oxygen and 
hydrogen gases are each kept in separate tanks or recep- 
tacles under heavy pressure, and are connected by rubber 
tubes to the jet where they combine. 



264 



MOTION PICTURE ELECTRICITY 



A cylinder of lime (about three-fourths of an inch in 
diameter) is placed in a vertical position in the three- 
pronged circular fork, near the opening of the jet, and the 
combustion of the combined gases on its surface creates 
a small disk of light of dazzling whiteness. The brilliancy 
of the rays proceeding from this light is so intense that 
they will illuminate the projected views over an area of 
25 or 30 feet square, if necessary. Owing to its extreme 
intensity it has great penetration, and is, therefore, the 



^my ^Sr ^P^ ^v 




Fig. 126 

most desirable illumination in halls of moderate size, and 
is almost indispensable for the largest churches, opera 
houses and theaters. No other light has ever been pro- 
duced which will equal it, everything considered, for 
magic lantern or stereopticon projection. 

DIRECTIONS FOR THE USE OF CALCIUM 
LIGHT 

Some operators use rubber bags for the storing of the 
hydrogen and oxygen gases, while some prefer to get their 
supply from the city gas companies in steel tanks made 
for that purpose, but for use in smaller towns and cities, 
the portable calcium light and gas-making outfit gives the 
most universal satisfaction. In either case, the receptacles 



MOTION PICTURE ELECTRICITY 265 

are provided with nipples for attaching the rubber tubes 
which are used to connect them with the calcium light jets. 

The tanks furnished by the city gas companies are 
painted to designate the kind of gas contained in each. 
The red tank contains the oxygen while the black tank 
contains the hydrogen gas. 

Slip one end of the rubber tube onto the nipple of the 
hydrogen gas tank or bag, and connect the other end with 
the left hand side of the jet. Connect one end of the other 
rubber tube with the oxygen bag or tank, and the other 
to the right side of the calcium jet. Now take a piece of 
lime from the box in which they are packed, and you will 
no doubt find that it is a little too large to go into the 
holder. Such being the case, take a knife and shave a 
little off of the three sides, leaving it just large enough 
so that the lime will fit snugly into the holder, then adjust 
it so it sets perfectly upright, and when it is revolved by 
the holder it will not vary too much from a perfectly 
upright position. 

The jet should now be placed in the lamp house, with 
the lime about three or four inches from the condensing 
lenses. 

Open the valve of the hydrogen tank, light the gas at 
the jet and turn on the hydrogen until the flame is from 
four to six inches high, then turn on a sufficient amount 
of the oxygen gas to almost consume the hydrogen flame. 
When the oxygen is turned on it creates a kind of 
whistling sound and this will continue until the right pro- 
portion of oxygen is mixed with the hydrogen. When 
the right proportion is reached, the light will burn without 
any noise whatever and almost no flame. If too much 
oxygen is turned on it will produce a roaring noise, and 
if the oxygen is allowed to flow too much in excess of its 
proper proportion, the light will extinguish itself with a 
sharp snap. Should this occur, it will be necessary to 
turn off the oxygen and immediately light the hydrogen, 
or turn both off and start anew. In adjusting the flow of 
oxygen in proportion to the hydrogen, it is necessary to 
turn the valves slowly, so as to be able to stop when the 



266 MOTION PICTURE ELECTRICITY 

right proportion is reached. The surface of the lime 
should be about one-eighth to one-fourth of an inch from 
the opening of the jet, to obtain the best results. 



ADJUSTMENT OF LIGHT 

Successful results in projection depend largely upon the 
correct adjustment of the lamp, which must throw a 
brilliantly illuminated circle upon the screen. 

After the objective is focused, as will be evidenced by 




Fig. 127 

a sharp clear image on the screen, remove slide and slide- 
holder, and examine the illuminated circle. If the light 
is centered and the lamp correctly adjusted this circle will 
be clear and entirely free from coloration or shadows. 

Fig. 127 illustrates the results of defective centering, 
showing the shadows and stating the causes. These can 
be speedily remedied and a little practice will soon make 
one adept in centering the light accurately. 

In Figs. 1 and 2 the radiant, i. e., the crater, needs to be 
properly adjusted laterally, it is too far to the right or left. 

In Figs. 3 and 4 it is too high or too low. 

In Fig. 5, 6 and 7 it is too near or too far from the 
condenser. 

Fig. 8 shows it to be in correct position, the field being 
entirelv clear. 



MOTION PICTURE ELECTRICITY 267 

These instructions hold good for the electric arc as well. 

The lime cylinder should be turned as often as every 
five minutes. Failure to do this is liable to form a pit in 
the surface of the lime, which may throw a tongue of 
flame against the condensers, and break them. Usually 
the light will begin to hiss when the surface is much pit- 
ted, and it should be immediately turned. If the opening 
in the point of the jet is too far away from the lime, it is 
liable also to cause hissing. 

Those who do not care to make their own gas, can get 
tanks from the large cities. They are supplied by the 
calcium light companies of this city at $6.25 per pair. A 
pair of tanks are supposed to last from four to six nights. 
To those who wish to use calcium light, we would recom- 
mend the "Model B" calcium gas-making outfit. The 
limes are unslacked, and should be kept in air-tight cans 
when not in use. The proper distance of the lime from 
the condenser will be found to be about three to three and 
one-half inches. 



"MODEL B" CALCIUM GAS MAKING OUTFIT 
WITH DIRECTIONS FOR OPERATING 

For convenience in shipping, the outfit has been taken 
apart, so as to pack it into small space. Take all parts 
from the case, loosen the thumb screws on the oxygen 
tank ( A) , let the bolts drop down and remove cover, after 
which the parts which are within may be removed. 

A charge of oxone may now be put into the holder (E) 
which is divided into compartments, arranged in spiral 
or step fashion. 

Beginning with the deepest pocket, insert the oxone 
cakes edgewise, using tongs provided with outfit. Each 
cake will generate enough gas to run the burner five min- 
utes, and from this it will be easy to determine the amount 
of oxone necessary for whatever length of time may be 
desired. 

The user is cautioned to handle oxone carefully, as it 
is a powerful alkali similar in nature to caustic soda, 



268 



MOTION PICTURE ELECTRICITY 




A — Oxygen Tank. 
B — Cover to Oxygen Tank. 
C-C-C — Thumb nuts and bolts for 
clamping down cover on Oxygen 

Tank. 
E — Holder for Oxone. 
F-G — Standpipe. 
H — Needle Valve on top of Satura- 

tor for controlling the flow of hy- 
drogen gas. 
I — Water Cock.. 
J — Water reservoir. The weight of 

water in this tank gives the gas 

sufficient pressure. 
I< — Overflow for Saturator. 
L — Removable screw cap on Saturator. 
N — Main cock or valve for oxygen 

■gas. 
— Needle valve on Saturator for 

controlling flow of oxygen gas to 

burner. 
P — Inlet to Condensing jacket (which 

surrounds Saturator) . In this 

chamber the moisture of Oxygen 

gas is condensed. 
S — Outlet of condensing chamber. 

From this point dry oxygen passes 

on up to controlling needle valves 

Hand 0. 

S-V— Safety Valve, in- 
serted in the rubber 
tubing on the Hydrogen 
Side to Plug T. 



Fig. 128 



m 



MOTION PICTURE ELECTRICITY 269 

strong lye, or potash, which would be very irritating if it 
came in contact with the skin. Do not touch it with the 
fingers, or with paper, cotton or woolen fabric, or other 
similar material, but handle only with wire tongs provided 
with the outfit. Equal care must be exercised in the mat- 
ter of allowing the hands to come in contact with the 
solution which is formed from the combination of water 
and oxone. Such portion of the cakes of oxone contained 
in the sealed tin can as are not placed in the oxone holder 
must be protected from the action of the atmosphere. 
When the oxone is left open to the action of the air it 
soon absorbs moisture and rapidly deteriorates. 

After holder (E) has been charged with oxone place 
the holder in tank (A). See that the rubber gasket or 
washer is in place in the groove around the edge of cover 
(B), place cover on tank, place bolts (C-C-C) in slots in 
the cover and tighten the nuts, giving the same reasonable 
and uniform pressure, so as to prevent escape of any of 
the oxygen gas. The two sections of standpipe (F-G) 
having been previously screwed together, the standpipe 
should then be securely screwed to cover (B), care being 
first taken to see that the rubber gaskets are in place so 
as to secure a gas-tight union. Now place the reservoir 
tank (J) in position, screwing it on the top of the stand- 
pipe, make sure that the main valve or gas cock (N) and 
the water cock (I) are closed, then pour clean water 
slowly into top of reservoir (J) until the level of same is 
within about two inches of the top of reservoir. About 
two gallons will be required. After the light has been 
started the water in reservoir will slowly sink into lower 
oxygen tank (A), and it will then be necessary to refill 
the reservoir (J) with water up to within about two or 
three inches of the top. No more zvater will then be nec- 
essary during the run. 

To Fill Saturator. — (This should never be done near a 
flame or fire.) Remove plug (T) and also the overflow 
cap (K). Insert funnel in opening at top and pour in 
slowly sulphuric ether until it begins to overflow at (K). 
While filling, it is, of course, necessary to keep the satura- 



270 MOTION PICTURE ELECTRICITY 

tor in an upright position. About ten fluid ounces will be 
required when saturator is charged for the first time. 
After filling, replace the cap screw (K) and the plug (T), 
securing same firmly in place. It is advisable to fill the 
saturator, say thirty minutes or so before using, so as to 
permit the fluid to thoroughly saturate the interior pack- 
ing. When gasoline is used make sure that nothing of a 
lower grade than 88 degrees is used. This cannot be ob- 
tained from drug stores and can only be had in a few of 
the large cities from responsible dealers in stereopticons, 
etc., and when ordering be sure to state that it is to be" 
used in a saturator. Where there is any doubt as to the 
quality of the gasoline it is advisable to use ether, which 
may be obtained anywhere. Do not change from one to 
the other without first drying out the saturator and filler 
thoroughly. 

The location of saturator on upright standpipe is best 
understood by reference to illustration. 

Now make sure that all valves are closed (N) (H) and 
(O) and then connect piece of rubber tubing from (N) 
to (P) and a shorter piece from (S) to (U), taking care 
to see that the tube is not kinked so as to choke the flow 
of gas. If the ends of tubing are first moistened with 
soapy water, it will be found easier to slip them on in 
place. 

The burner in lantern may now be connected to satura- 
tor at outlets (T) and (O), as follows: The metal con- 
nection (S-V) inserted between the two pieces of rubber 
tubing is a safety valve similar to hydrogen plug (T), 
and is used with the short piece of rubber tubing next to 
the jet on the left hand side of the calcium jet or burner. 
The opposite end of the longer piece of tubing being at- 
tached to the hydrogen plug (T). 

The longest piece of tubing is attached to the oxygen 
cross valve (O) , and to the right hand side of the calcium 
jet or burner. Put a fresh lime in burner, allowing a 
space of about 3/16 of an inch between surface of lime 
and terminal of goose neck (or outlet). 



MOTION PICTURE ELECTRICITY 271 

To Start the Light.— Open the main valve (N), then 
slowly open the needle valve (H) on top of saturator, 
and apply a lighted match to burner, allowing the flame 
to extend two or three inches above the tip of the burner, 
then slowly open needle valve (O) until the gas from that 
source forces the hydrogen flame gently against the lime. 
Several minutes will be required to permit the air (which 
is in the oxygen tank at the start), to pass through the 
burner, after which pure oxygen gas begins to form and 
pass to the burner. The light will then become brilliant, 
and its maximum power may be obtained by adjusting 
the valves (H) and (O), until hissing is stopped, and the 
surface of the lime presents an intensely brilliant spot of 
light. 

Notice — We advise the use of ether only, as 88° gas- 
oline is no longer made. 

USE CONCENTRATED ETHER ONLY 

The supply of saturator gas to burner should be a little 
in excess of the oxygen. The presence of a small fringe 
of reddish flame at lime will indicate this. 

Hissing or roaring is caused by an excessive supply of 
one or both gases, and can be stopped by adjusting the 
needle valves. When the proper adjustment is secured, 
the light will burn with but little or no attention. After 
the outfit has been used once or twice the operator will 
have no difficulty in securing a beautiful, steady and bril- 
liant light. 

Snapping and popping is caused by too great a supply 
of oxygen and not enough hydrogen, or it may be caused 
by the fluid supply in saturator running low. About four 
ounces of fluid per hour is required in saturator, and it is 
advisable to fill saturator each time it is used, taking 
care, of course, to see that overflow screw (K) is removed 
while filling. Should one of the rubber tubes be blown 
off with a loud report it. is almost certainly due to an 
empty saturator. While the effect is harmless it is apt 
to startle an audience, and for this reason it is well to see 



272 MOTION PICTURE ELECTRICITY 

to it that saturator is properly charged before beginning 
an exhibition. 

When through with the light turn off the main valve 
(N) first, then the needle valve (O) and lastly (H). A 
series of short, snapping sounds may occur when light is 
extinguished, but these are harmless. This is due to the 
small amount of gas remaining in the tubes which comes 
in contact with the hot surface of the lime. Also discon- 
nect burner tubes from saturator. If through with the 
light, drain off water (if any), from water cock (I), dis- 
connect tube from valve (N) and unscrew reservoir (J). 
Now disconnect rubber tube at (S) and slip it over plug 
(T) ; this prevents any ether vapor escaping when sat- 
urator is not in use. Now unscrew the standpipe (G) to 
which saturator is clamped, and drain out through (S) 
any water which may have formed in the jacket surround- 
ing the saturator. 

The iron cover on oxygen tank (A) may now be re- 
moved, and the tank emptied, after which it should be 
rinsed out in running water, and wiped with an old cloth. 
The standpipe and reservoir (J) should also be rinsed 
out and wiped, and all parts kept clean and dry. 

Be careful at all times not to lose the rubber gaskets or 
zvashers, which are necessary to prevent leakage. 

Also be careful to see that lead gaskets at (K) and (T) 
are in place. 

When setting the apparatus up for use, make sure that 
these are all in place, particularly the large rubber ring 
fitted in recess of cover, which should be flat and even y 
and not twisted. 

After saturator has been used a dozen times or so the 
interior filler made of a roll of white flannel should be 
removed and dried out in the sun out of doors away from 
flame or light. This is advisable for the reason that gas- 
oline and ether contain a certain amount of non-evaporat- 
ing substance which remains in saturator and accumulates 
by repeated use. The lower cap of saturator may be re- 
moved by applying wrench at (L). When this cap is 



MOTION PICTURE ELECTRICITY 273 

again replaced make sure same is started right on the 
thread. This is important in order to secure a perfectly 
leak-proof joint. - 

Extra flannel fillers for saturator, each 75c. 

Material used for generating the gas : 

Oxone, per can of 16 cakes $1-35 

Sulphuric ether (pure) in sealed pound cans. . . .65 

Limes, % in. x 2 in. in cans of 12 90 

Limes, 1% in. x 2 in. in cans of 12 1.80 

and water for the upper tank. 

We recommend the use of 1% in. limes, as they admit 
of a larger field of incandescence and consequently pro- 
ject a brighter light of greater power than the smaller 
limes and last fully two-thirds longer than the smaller 
limes. 

// is advisable to use jet {burner) of small bore. Not 
larger than No. 56 drill gauge. Large bore jets waste gas 
and do not improve light. 

At the above cost of renewals the expense of operating 
calcium jet is from 90 cents to $1.00 per hour for either 
stereopticon or moving picture machine. 



MOTION PICTURE ELECTRICITY 275 



Index of Contents 



PAGE 

A. C. Economizer 134 

Adjustable Type of the Rheostat 147 

Advertising Value of an Electric Sign 93 

AL Rectifiers 225 

Alternating Current 3 l 

Alternating Current Automatic Electric Type Hallberg 

Economizer 194 

Alternating to Direct Current, For 203 

Alternations 42 

Ampere 11 

Arc Voltage Limit 139 

Arrangement of Electric Circuits and Lamps 85 

Calculating Resistance 140 

Carbon Setting 171 

Carbon Setting, Correct D. C 119 

Carbon Setting, Judgment in Making 121 

Carbon Setting, Right Angle Arc 115 

Carbon Setting — the Right Angle Arc — Variable 

Angle Setting 1 15-1 16 

Carbon Setting for Tilted Projectors 124 

Carbon Setting, Variable Angle 116 

Constant Current Transformer 51 

Constant Potential Transformer 47 

Constant Potential Windings 52 

Correct D. C. Setting of Carbons 119 

Current, Alternating 31 

Current, Direct 23 

Current, Generation of 23 

Cycles 40 

Cycles per Second 43 

D. C. Motor-generators 165 

Decorative Front Lighting 93 

Direct Current 23 

Direct Current Projection 103 

Directions as to Reading Meters 81 

Double Multiple— Rheostat 152 

Electric Sign, Advertising Value of 93 

Electric Sign, The 93 

Electrical Service 59 

Electricity 9 

Emergency and Exit Lightings , 89 



276 MOTION PICTURE ELECTRICITY 

Index of Contents 

Examples of Difficult Meter Readings 82 

Expert Advice on Theater Wiring 91 

Flaming Arc, The 92 

Formulas 20-21-22 

Generation of Current 23 

Hallberg A. C. toD. C. Economizers 200 

Hallberg Alternating Current Economizer Data 198 

Hallberg Automatic Electric D. C. Economizer, In- 
structions for Setting and Operating 215-216-217 

Hallberg Direct Current Economizer Data 210 

Hallberg Economizer, The 194 

Hallberg Economizer, Automatic Direct Current Type — Spe- 
cial Information and Instruction 209 

Hidden Crater 119 

How to Read an Electric Meter 79 

Incandescent Lamp Type 157 

Instruction for Installing and Operating 224 

Instruction for Operating Hallberg A. C. to D. C. 

Economizers 204 

Interior Fixtures 96 

Interior Service 64 

Isolated Electric Lighting Plants 226 

Judgment in Making Settings of Carbons 121 

Kilowatt Hour 17 

Lighting, Decorative Front 93 

Lighting, Emergency and Exit 89 

Lighting Fixtures and Lamps 92 

Lobby Illuminations ' 94 

Meter, How to Read an Electric 79 

Meter Readings, Examples of Difficult 82 

Meter, Recording Watt-hour 

Meters, Directions as to Reading 81 

Methods of Connecting — Rheostat 151 

Multiple Series for 220 Volts 155 

Non-adjustable Type of the Rheostat 145 

Ohm 12 

Operating Room Circuits 90 

Over-prominent Crater — Carbons 120 

Outside Illumination 92 

Practical and Commercial Section 193 

Practical Suggestions 235 

Practice of Resistance for 60 volts, 75 volts, no volts, 

220 volts, 550 volts 134-136 

Principal of Operations, Westinghouse-Cooper 

Hewitt Rectifiers ._ ; 218 

Problem 1 to Problem 5 of Calculating Resistance 140-141 

Recording Watt-hour Meter, The 71 

Rectifier, Instruction for Installing and Operating 224 

Rectifier, Principal of Operation 218 



MOTION PICTURE ELECTRICITY 277 

Index of Contents 

Resistance 129 

Resistance, Calculating 140 

Resistance, Calculating Problem 1 to Problem 5 140-141 

Rheostat, Adjustable Type 147 

Rheostat, Double Multiple 152 

Rheostat, Incandescent Lamp Type 157 

Rheostat, Methods of Connecting 151 

Rheostat, Non-adjustable Type 145 

Rheostat, Single Multiple 152 

Rheostat, Special Types 156 

Rheostat, Storage Battery Type 159 

Rheostat, The 143 

Rheostat, Triple Multiple 153 

Rheostat, Water Type 161 

Series for 220 Volts 154 

Settings for Tilted Projectors 124 

Single Multiple — Rheostat 152 

Special Direction for the Hallberg A. E. E. A. C. Standard 

Type 199 

Special Information and Instructions for Hallberg A. C. to 

D. C. Economizers 200 

Special Types — Rheostat 156 

Stage Circuits 90 

Storage Battery Type 159 

Street Service 59 

Testing Voltage 10 

Theater Wirings 85 

Theory of Resistance 129 

Three- wire System for Direct Current 27 

Transformer, Constant Current 51 

Transformer, Constant Potential 47 

Transformer for Alternating Current, The 47 

Triple Multiple, Rheostat 153 

V. A. C. Generator 43 

Variable Angle Setting of Carbons 116 

Voltage 10 

Voltaic Arc, The 107 

Water Type Rheostat 161 

Watt 15 

Westinghouse-Cooper Hewitt Rectifiers 218 

Wiring, Expert Advice on Theatre 91 

Wiring, Theatre 85 



278 MOTION PICTURE ELECTRICITY 

Index of Practical Suggestions 

Data and Tables for Projection 

Adjustment of Light 266 

Allowable Carrying Capacity of Copper Wires 239 

Approximate Prices for Fans 252 

Brightness of Various Illuminations 245 

Calcium Light 263 

Centigrade and Fahrenheit Scales 256 

Comparative Resistance of Various Metals 245 

Comparison of Light 250 

Connecting Moving Picture Machine and Stereopticons for 

Traveling Exhibit 237 

Cost of Electric Signs 248 

Cost of Operating an Electric Sign per Hour 250 

Current per Phase in Various Systems 244 

Current Required for Motion Picture Projection 238 

Current Required for Stereopticon Projection 238 

Decimals of an Inch for Each One-Sixty-fourth 261 

Diameter, Weights and Resistance of Copper Wire 240 

Directions for the Use of Calcium Light 264 

Effect of Heat on Materials 256 

Electric Signs 247 

Energy Radiation 247 

Equivalents of Electrical Units 243 

Fans and Blowers 251 

Figuring Proper Size of Wire ■. . 241 

Heat Units 258 

Heating Values for Liquid Fuels 259 

High Temperatures Judged by Color 257 

Machine Switches 236 

"Model B" Calcium Gas Making Outfit with Directions for 

Operating 267 

Reduction in Size of Line Wire, Fuses and Switches With 

the Hallberg Economizer 236 

Size of Wire for Stereopticon, Spotlight and Motion Picture 

Machines 2^7 

Strength of Materials 255 

Table for Film Projection ..-..■ 262 

Table for Stereopticon Projection Lenses 263 

Table of Coefficients. 246 

Table of Specific Resistance 244 

Table Showing the Difference Between Wire Gauges 242 

To Find Amperes^ per Phase 243 

To Find the Positive Crater of a D. C. Arc 236 

Use Concentrated Ether Only 271 

Weight of Materials and Liquids 260 

Weights and Measures 253 to 255 



MOTION PICTURE ELECTRICITY 279 



Index to Advertisements 



"HALLBERG" A. C. Economizer 280 

"BAIRD" M. P. Machines.... 281 

"HALLBERG" M. P. Machines 282 

NICHOLAS POWER COMPANY 283 

"HALLBERG" Terminals and Slides 284 

"SIMPLEX" Projector 285 

"HALLBERG" D. C. to D. C. Economizer 286 

AMERICAN "STANDARD" M. P. Machine 287 

WAGNER ELECTRIC CO 288 

WESTINGHOUSE ELECTRIC CO 289 

CHAS. STRELINGER 290 

HUGO REISINGER 291 

"HALLBERG" Supplies 292 

AMUSEMENT SALES 293 

MIRROR SCREEN COMPANY 293 

KLIEGL BROTHERS 293 

CHALMERS PUBLISHING CO 294 

CHALMERS PUBLISHING CO 295 

CHALMERS PUBLISHING CO 296 

MOVING PICTURE WORLD 297 

CHALMERS PUBLISHING CO 298 

J. H. HALLBERG.. 299 



>8o 



MOTION PICTURE ELECTRICITY 



HALLBERG 
A. C. ECONOMIZER 

was the first and is still the best A. C. 
saver in the World. 

Ask any up-to-the- 
minute operator ! 

I have several thou- 
sand in use every day. 

Where you cannot 
afford the Hallberg A. 
C. to D. C. put in the 
Hallberg Straight A. C. Type. 

Send for free circulars 

HALLBERG 
Condensing Lenses 

are the best imported, carried in 
stock in the following foci : 

6^-7-7^-8-8^-9-9^ and 
1 inches 4^ diam. 

Also for Spot Lights : 6J^ - 7^ 
83^- 10 and 12 inch foci 5" and 6" diameter. 

J. H. HALLBERG, 36 E. 23rd St., New York, H.T. 

ECONOMIZER DEPT. 





MOTION PICTURE ELECTRICITY 



281 



DairD 



Absolutely eliminates flicker. 

Handles 3000 feet of film. 

The latest, most magnificent and most expen- 
sive motion picture machine ever constructed in 
the world. 




Baird Motion Picture Machine Co. 

24 East 23rd Street New York 



282 MOTION PICTURE ELECTRICITY 


I SELL 


BAIRD 


EDISON 


MOTIOGRAPH 


POWER'S 6A and 


SIMPLEX 


MOVING PICTURE 


MACHINES 


and Guarantee] 
RESULTS 


Send for free Catalogues. } 


I U HAflUEBf 36 E. 23rd St. 
J. 11. nALL.DE.Kl), New York, N.Y. 

MACHINE DEPT. 



MOTION PICTURE ELECTRICITY 283 




A large majority of the entire 
motion picture trade appre- 
ciate the 

HIGH EFFICIENCY 

DURABILITY 

PERFECT PROJECTION 

OF 

POWER'S CAMERAGRAPH 

No. 6A 

NICHOLAS POWER COMPANY 

Ninety Gold Street New York City 



284 



MOTION PICTURE ELECTRICITY 



HALLBERG 

Pure Copper M. P. Terminals 

For M. P. Lamps 

Save burnt out 
leads and poor 
light. Cut 
your expense 
for lugs in half. 
Get a pair — 
state make and 
type of ma- 
chine. 
$1.50 by mail 

HALLBERG 

Exclusive Announcement Slides 

Are Nobby, Beautiful and Original 

They cost 50c each 
6 for $2.70 12 for $4.80 

I have 14 different Good Night Slides. 
Buy 6 or more so you will never have to 
show the same slides over once a week. 
Try the effect — hear the favorable com- 
ments. 

J. H. HALLBERG 

36 East 23rd Street NEW YORK, N. Y. 

SUPPLY DEPT. 




MOTION PICTURE ELECTRICITY 



285 



JIIIIIIIIIIIIIIIIIIIIIII!lll!llllllll!llilllllllilll!IIIIIIIIIIMIIIill!l!!3lllllU 

[ SIMPLEX I 

| Motion Picture Projector and Camera 

= Each recognized as peerless in its own | 
= particular field. 

Simplex projectors are now used in the 5 

= foremost theatres all over the world and S 

I are the choice of the most successful and S 

= particular exhibitors on account of their S 

= rock-steady, flickerless pictures, resistance = 

I to wear and dependableness. = 

= Simplex motion picture cameras are in = 

S keeping with the projector in simplicity, § 

S excellence of materials and workmanship, = 

I and the high quality of their work. Fur- = 

I nished complete with tripod, high grade = 

I lens and carrying case. Just the thing = 

S for anyone who wants an inexpensive = 

but good outfit to take local events at = 
short notice. 

Simplex is the ap- | 

paratus for you to use | 

for taking and project- = 

ing motion pictures. | 

Made and Guaranteed by ~ 

THE PRECISION I 

MACHINE CO. | 

317 E. 34th St. New York I 




nillllllllllliliilllilllllliliiiiiiiiiiiiiiiiiiiiiiiniiiiiiiiillliiiiiiiiiiiiiiiii 



286 MOTION PICTURE ELECTRICITY 

HALLBERG 

D. C. to D. C. ECONOMIZER 

Does away with the Hot 
Wasteful Rheostat on all 
Direct Current Circuits 

Guaranteed 
Saving: 

40-50% on 11 Ov 

65-75% on 220v 

80-90% on 550v 

also made 

for Engine 

Drive to make 

your own current for Travelling or regular Shows: 




I Also Sell The 

CELEBRATED "BRUSH" 

Electric Lighting Sets for 
Kerosene or Gasoline 

Send for free Circulars 

J. H. HALLBERG 

36 E. 23rd St. New York, N. Y. 

ECONOMIZER DEPT. 



MOTION PICTURE ELECTRICITY 287 



This Page Reserved 
for 

AMERICAN 
"STANDARD" 

MOVING PICTURE 

MACHINE CO. 



New York, N. Y. 



288 MOTION PICTURE ELECTRICITY 

Good Brilliant 

PICTURES 

fill the house. The goodness of the 
pictures depends upon selection of the 
films — 

Brilliancy of Pictures 

is assured by the use of the 

It converts the 
usual alternating 
current supply to a 
steady direct cur- 
rent, the best cur- 
rent for moving 
picture projection. 

Wagner Converter is easy to install and easy to 
operate. It is rugged and reliable, and its first 
cost is its last cost. Our Bulletin 103F and 
Booklet "Standing Room Only" are yours for 
the asking. 

WaaTir^^^ rMaTiiifaAiiriri2Companv> 

Saint I/ouis, Missouri 




MOTION PICTURE ELECTRICITY 289 




Not a Flicker 
On the Picture 

when the light is projected by a direct- 
current arc lamp. 

Increase your patronage by using direct-current 
lamps on alternating current supply circuits 
with a — 

Westinghouse 
Cooper-Hewitt Rectifier 

It changes alternating current to direct current. The 
rectifier occupies little space and operates automatically. 
There are no moving parts — no machinery to get out of 
order — no dirt — no noise. Read all about it in Folder 4205. 

Westinghouse Electric & Mfg. Co. 

East Pittsburgh, Pa. 

Sales Offices in 45 American Cities 



290 MOTION PICTURE ELECTRICITY 

THE BRUSH 

Electric Lighting Set 




ESPECIALLY adapted to the making of 
a perfect Direct Current for projection 
work. Made in sizes of 2, 4 and 10 kilo- 
watts, Direct-connected, comparatively 
light, Durable and Economical. 

Either 60-65 or 110-115 volts. 

Our 125 page catalogue gives much 
useful information about Isolated 
Electric Lighting Plants, and may 
be had for the asking. 

THE CHAS. A. STRELINGER CO. 

BOX M. P.-4 DETROIT, MICH., U. S. A. 





MOTION PICTURE ELECTRICITY 291 



PINK LABEL 



PROJECTION OF CLEAR, 
WELL-DEFINED PIC- 
TURES depends entirely on 
the quality of light behind the film. 

Your machine may be of the latest 
improved type, your film of the 
best, but without a brilliant, steady 
arc, perfect results are impossible. 

It is therefore essential to pay care- 
ful attention to the quality of the 
carbons used and it is poor policy 
to buy any but the best. 

You make no mistake when you 
buy "Electra" Pink Label Projec- 
tor Carbons. They are conceded 
to be the Standard for quality. A 
trial will convince you. 

Sole Importer 

HUGO REISINGER 

11 BROADWAY 
NEW YORK 



PINK LABEL 





2Q2 MOTION PICTURE ELECTRICITY 



I 






GUNDLACH M. P. LENSES 
BAUSCH & LOMB LENSES 
' « ELECTRA " CARBONS 

" BIO " CARBONS 

" FRENCH " CARBONS 



NEW and USED RHEOSTATS 
Special Rheostats to Order 



ASBESTOS-COVERED M. P. CABLE 



NEW and USED " COMPENSARCS' 



POWER'S INDUCTORS and CHOKE- 
COILS OF ALL KINDS 



FILM CEMENT f Tb! 11 B « u %i5S5 

MP Off Small Can, 25c. 
• 1% KJIU j lb . Bottle, 75c. 



FILM REELS, FIRE PROOF 
CABINETS and REWINDERS 



For Large Catalogue send 25c. 



J. H. HALLBERG 

36 East 23d Street New York, N. Y, 

Supply Dept. 



MOTION PICTURE ELECTRICITY 



293 



We are the Largest Manufacturers of all kinds of 
Theatre Devices for Theatre Entrances 

We sell these Devices all over the World. 

We manufacture devices to sell tickets, 
devices to receive tickets, devices to de- 
stroy tickets, devices to sell checks and 
devices to receive them, and with our sys- 
tems installed at your ticket window and at 
your door we eliminate all chance of leaks, 
establish a rapid method of handling 
patrons and will make your Theatre up-to- 
date in every way. 

The leading dealers of the country 
handle our devices. 

Write for catalog. 

AMUSEMENT SALES CO. 

Woodward & Warren 
DETROIT, MICH. 




The Mirror Screen Company of Shelbyville, Ind. 

Make Every Kind of Screen for Moving Picture Projection 
GLASS SCREENS METALLIZED SCREENS 

MIRROR SCREENS GOLD FIBRE 

MIRROR SCREENS, in Two Pieces SILVER FIBRE 

TRANSPARENT SCREENS MIRROR CLOTH 

PURE WHITE OPAQUE 
The "Mirror Screen" is the only surface that is 
proper and perfect to project Moving Pictures on, 
because it reflects light alone by Diffuse Reflection. 
Get a Glass " MIRROR SCREEN " and Save the Eye 



Universal Electric Stage Lighting Co. 



Everything Electrical 
for Theatres, Pro- 
ductions 

Manufacturers of Arc 
Lamps and Effects 




Proprietors 

238-240 West 50th Street 



New York 



294 MOTION PICTURE ELECTRICITY 



OLDEST, LARGEST AND BEST 
MOVING PICTURE WEEKLY IS THE 

Moving Picture World 

Founded by J. P. CHALMERS 



Weekly Departments as follows: — 

Release Dates 

Reviews, Comments 
and Synopses 
of all Films 

made or sold 
in America 

Projection Department 

Educational Department 

Advertising for Exhibitors 
Foreign Trade Notes 

Exhibitors League Page 
Music for the Pictures 

Photoplaywright Section 

Correspondence, Etc., Etc. 

Advertisements of Leading 

Film Manufacturers, Exchanges and Importers 
Machine Manufacturers and Dealers 

Manufacturers of Electrical Equipment 
Theatre Seating and Principal 

Dealers in Moving Picture Supplies 



YEARLY SUBSCRIPTION RATE 

Domestic $3.00 Canada $3.50 Foreign $4.00 



CHALMERS PUBLISHING COMPANY 

Box 226, Madison Sq. P. O. New York City 



MOTION PICTURE ELECTRICITY 295 

F. H. RICHARDSON'S 

Motion Picture 

HANDBOOK 

For Managers and Operators 
Second Edition 430 Pages 



Complete instruction on the EDISON, MOTIO- 
GRAPH, POWERS, SIMPLEX and STANDARD 

machines with detail illustrations of all parts. 

Chapters on Electric Wiring and Insulation, Electric 
Economizers, Transformers and Generating Sets, 
Resistance Devices, Lenses, Carbons, Screens, Stere- 
opticons, Theatre Lighting and General Equipment, 
etc., etc. 

The most thorough, comprehensive and complete 
book on the subject of Projection. Profusely illus- 
trated and handsomely bound in dark-red cloth- 
board covers. 



$2.50 Per Copy, Post Free $2.50 

Kindly address all orders and remittances to 

Chalmers Publishing Company 

Box 226, Madison Square P. O. New York City 



296 MOTION PICTURE ELECTRICITY 



The Chalmers Standard 

Moving Picture Publications 

The most instructive book on the preparation and 
writing of Photoplay scenarios is 
Epes W. Sargent's 

Technique of the Photoplay 

1 80 pages in Clothboard Binding. 
$2.00 per Copy. Postage Free. 

The best known and most widely circulated mov- 
ing picture weekly in the world is the 

Moving Picture World 

Founded in 1907 by J. P. Chalmers. Yearly 

Subscription Rates: Domestic, $3.00; 

Canada, $3.50; Foreign, $4.00. 

The Standard book on moving picture projection 
and operating is the 

Motion Picture Hand Book 

FOR MANAGERS AND OPERATORS 

By F. H. Richardson 

420 Pages in Clothboard Binding. 
$2.50 per Copy. Postage Free. 

Motion Picture Electricity 

By J. H. Hallberg 

The comprehensive and exhaustive work here- 
with submitted to the moving picture public. 
$2.50 per Copy. Postage Free. 
Address all communications, orders and 
remittances to 

Chalmers Publishing Co. 

Box 226, Madison Square P. O. New York City 



<t\ 



MOTION PICTURE ELECTRICITY 297 

Picture Machine Operators 

and 

Students of Projection 

will find the weekly Department 
on 

Projection 

in the 

Moving Picture W>rld 

of great assistance. It is up-to-date 
and deals with problems of opera- 
tors in all parts of the country and 
under all sorts of conditions, and it 
is conducted by F. H. Richardson. 
The information in as ingle issue may 
be worth a year's subscription to you. 

Address remittances for subscriptions as 
below : 

Domestic .$3.00 per year 

Canada 3.50 " " 

Foreign 4.00 " " 

Moving Picture World, SFfeJS 



298 MOTION PICTURE ELECTRICITY 

The present second editions of two of our pub- 
lications are meeting with such a ready sale that 
they will soon be exhausted. New editions of 
both the 

MOTION PICTURE 

HANDBOOK 

By F. H. Richardson 

and of the 

TECHNIQUE 

of the 

PHOTOPLAY 

By Epes W. Sargent 

will soon be necessary and they will probably be 
larger and more expensive books. For infor- 
mation and prices on any of our publications, 
kindly write direct to 

CHALMERS PUBLISHING CO. 

17 Madison Ave., New York City 



MOTION PICTURE ELECTRICITY 299 



HALLBERG 

A. C. to D. C. ECONOMIZER 

Gives the Best Light — Saves the Most 




Is used by all leading exhibitors who understand 
the value of the most brilliant and steady light 
to be obtained. The HALLBERG makes your 
pictures lifelike by bringing out the details in 
the shadows which are never seen on the screen 
with ordinary light. 

Get wise — put one over on your competitor — 
please your patrons and give your operator a 
treat by putting in a HALLBERG A. C.-D. C. 
Economizer. 

Send for Free Circular 

J. H. HALLBERG Ee T$™ 

36 E. 23rd Street NEW YORK, N. Y. 



